Final Journal of the Indian Roads Congress

Volume 74-3

October - December 2013

`

20.00

JOURNAL OF THE INDIAN ROADS CONGRESS VOLUME 74-3 CONTENTS

Page

Highlights of the 1st Regional Workshop on “Promoting Usage of New Materials/Techniques/T Materials/Techniques/Technologies/ echnologies/ Equipment in Road Construction” held at Bengaluru (Karnataka) on 23-24 October, 2013

243

Paper No. 600 “Distresses in Cement Concrete Pavements – A Case Study” A.K. Mishra, Renu Mathur, Rakesh Kumar, J.B. Sengupta and Dinesh Ganvir Paper No. 601 “Rehabilitation and Upgradation of an Existing Aireld Runway Pavement for Operation of Next Generation Aircrafts”

251

Rahul Oberoi and A. Veeraragavan Taken on Caisson Foundations and Cutting Edge Construction at Paper No. 602 “Case Study on New Initiatives Taken

Bogibeel Bridge” Anupam Das Paper No. 603 “Landslide Hazard Database and Inventory- Focus on a Suitable Methodology for India” Shanal Pradhan, Kishor Kumar and S. Gangopadhyay Paper No. 604 “Evaluation of Design of Geocell Reinforced Unpaved Roads” Jyothi P. Menon and G.L. Sivakumar Babu Paper No. 605 “Analytical Design of Short Panelled Concrete Pavements”

M.V. Arun Chand and B.B. Pandey

Paper No. 606 “Detailing Provisions of

IRC:112-2011 IRC:112-2011 Compared with Previous Codes (i.e. I RC:21 & IRC:18)”

269

289 304 315 322

329

© The Rights of Publication and Translation are reserved.

The Indian Roads Congress as a body does not hold

HIGHLIGHTS OF THE 1 st REGIONAL WORKSHOP ON 243 HIGHLIGHTS OF 1 R EGIONAL EGIONAL WORKSHOP "PROMOTING USAGE OF NEW MATERIALS/ TECHNIQUES/ TECHNOLOGIES/ EQUIPMENT IN ROAD CONSTRUCTION" HELD AT AT BENGALURU (KARNA (KARNAT TAKA) ON 23-24 OCTOBER, 2013 ST

Receiving and Welcoming Dignitaries

Shri Oscar Fernandes ji, Hon’ble Minister of Road Transport & Highways being welcomed at Venue by Dr. H.C. Mahadevappa ji, Hon'ble Minister of Public Works, Govt. of Karnataka

Hon'ble Minister of Road Transport and Highways Shri Oscar Fernandes ji, Mrs. Fernandes and other dignitaries on the way to Conference Hall

244

HIGHLIGHTS OF 1ST R EGIONAL EGIONAL WORKSHOP

The Indian Roads Congress (IRC) in association with Public Works, Ports and Inland Water Deaprtment, Govt. of Karnataka organized two days' Regional Workshop Workshop on "Promoting Usage of New Materials/Techniques/Technologies/ Materials/Techniques/Technologies/ rd th Equipment in Road Construction" on the 23 & 24 October, 2013 at Gayathri Vihar, Palace Ground, Bengaluru. The Regional workshop was attended by more than 500 Highway Sector Engineers/ Professionals from all Stakeholders namely the State and Central Government Departments/Organisations, Municipal Corporations, other local bodies, the Consultants/Contractors, Concessionaires, etc from States of Karnataka, Kerala, Goa and Maharashtra. Glimpses of Inaugural Function


Shri Oscar Fernandes ji, Hon’ble Minister of Road Transport & Highways being welcomed in Traditional Manner by Dr. H.C. Mahadevappa ji, Hon'ble Minister for Public Works, Govt. of Karnataka

245

Shri Oscar Fernandes ji, Hon’ble Minister of Road Transport & Highways being presented mementos by Dr. H.C. Mahadevappa ji, Hon'ble Minister for Public Works, Govt. of Karnataka

246


Release of Souvenir

Shri Oscar Fernandes, Hon’ble Union Minister of Road Transport & Highways, Govt. of India released Souvenir published on the occasion of the rst regional workshop on “Promoting Usage of New Materials/ Techniques/Technologies/Equipment in Road Construction” containing messages from the dignitaries and technical presentations delivered during the workshop.


247

List of Technical Presentations made during the Regional Workshop Workshop

Workshop, a total of 17 number of T echnical Presentations were made by the experts on the New Technology/ Techniques/ Techniques/ Equipment/New Materials, etc. The same were well received by the participants who have

During 2 days'

suggested to make this a regular feature: 1. 2. 3. 4. 5. 6.

7. 8. 9.

“Retro-reective Material for Road Safety Signage” by Shri John Crotty, Senior Applications Engineer & Shri Daniel Berger, Director, Quality, Quality, Research & Development, M/s. ORAFOL Europe GmbH, Ireland. “Towards “Towards Forgiving Highways – New Technologies for Highway Safety” by Shri Param Preet Singh, Director, M/s. Avantech Avantech Engineering Consortium Pvt. Ltd., New Delhi. “Processed Steel Slag as Alternate Alternate Aggregate for Flexible Flexible Pavements” by Shri Rajanikanth Reddy, Reddy, Senior Manager, Slag Co-Products, Harsco India Pvt. Ltd., Hyderabad. “Typical “Typical Cases of Load Tests Tests on Bridges” by Shri Sudarshan Iyengar, Senior Director, CIVIL AID, Bangalore. “Wire Rope Safety Fence”by Shri V. Eshwaran, General Manager - Business Development, Hill & Smith Infrastructure Products India Pvt. Ltd., Gurgaon. “Innovative Geotechnical Solutions” by Shri Sharokh P. Bagli, Chief Technology Ofcer, Strata Geosystems (India) Pvt. Ltd., Ltd., Mumbai. Mumbai. “Rehabilitation of Bridges” by Sh ri Mohan Koti, GM (Tech.), (Tech.), Binyas Contech Pvt. Ltd. “Application of Geo Textiles in Road Constructions and Some Case Studies” by Prof. B.R. Srinivas Murthy, Retd. Professor, IISC, Bangalore. “Use of Nano Technology in Road Construction” by Shri Ganesh Hegde, DGM (Projects), Zydex Industries, Bangalore.

248


Dr. H.C. Mahadevappa ji, Hon’ble Minister for Public Works, Govt. of Karnataka inaugurating the Technical Exhibition

Dignitaries interacting with Exhibiters at the Technical Exhibition


DG (RD) & SS and President, IRC having a Discussion with the Experts

249

Dr. H.C. Mahadevappa ji, Hon'ble Minister for Public Works, Govt. of Karnataka having Discussion with Dr. E. Venkataiah, Principal Secretary to Govt. of Karnataka, PWP & IWTD and Shri Vishnu Shankar Prasad, Secretary General, IRC

Paper No. 600

DISTRESSES IN CEMENT CEME NT CONCRETE PAVEMENTS – A CASE STUDY ENU MATHUR *, AKESH K UMAR UMAR *, A.K. MISHRA*, R ENU *, R AKESH *, J.B. SENGUPTA* AND DINESH GANVIR *

SYNOPSIS Since last one decade construction of rigid pavements is gaining popularity. However, some failures are also observed in the recent past. One such case is of Fatehpur –Kokhraj section of NH-2. The 58 km long road stretch was constructed in 2004 by NHAI. The paper presents the results of eld investigations carried out to ascertain the causes of distresses and the remedial measures suggested.

1

INTRODUCTION

The Rigid pavement on Allahabad Bypass from km 100 to 158 (Fatehpur –Kokhraj section) of NH-2 was constructed in 2004 (km100 to 115- package IIC and km 115 to 158- package IIIA). The total length of the section is 58 km with chainage km 570.753 to 628.753. With passage of time NHAI observed the development

•

Selection of panels to be rehabilitated or replaced and to suggest the remedial measures to prevent further deterioration of the cracked panels.

•

To provide suitable techniques for rehabilitation of severely distressed panels.

3

FIELD INVESTIGA INVESTI GATION TION

252

MISHRA, MATHUR , K UMAR UMAR , SENGUPTA AND GANVIR ON ANVIR ON

km 585.753 to 628.753, short length to full length longitudinal cracks (>1 m) were observed. •

At chainage 586 to 588, 622-623, 623-624 full length longitudinal cracks were observed extending to several slabs. (Photo 4-5).

DISTRESSES I N CEMENT CONCRETE PAVEMENTS –A CASE STUDY has further propagated to several slabs ahead.

•

(Photo 6).

253

Badly deteriorated patches of partial depth repair

were also observed at chainage 607.250 which requires immediate attention for repair. •

Lane to median separation, approximately of

18 m length was observed at chainage 585.387 to 585.405. •

Rain cuts gullies were also observed at many places along the earthen shoulder shoulder..

3.2

Criteria for the Selection of Core Extraction

After completion of crack mapping of the entire stretch,

Photo 6 Cross Stitching at chainage-585.800 •

A transverse crack with spalled edges was observed at chainage 603.805 (Photo 7).

cores were extracted at the longitudinal and transverse cracks to determine the depth of the cracks. Cores were also extracted from the transverse, longitudinal and tied

shoulder joint locations to assess the propagation of the joint cuts in the pavement. Cores were also taken from the sound (Photo 8) and cracked panels to determine the strength of the PQC. Total 54 cores were extracted from the entire stretch. The core bit of 100 mm and 150 mm diameter were used for extracting the cores.

254


9

11

579.430, crack, outer lane

0.5 to 1.00

146

330

-

-

10

12


0.50 to 1.00

30

312

-

-

11

13

580.910, longitudinal joint

-

Full depth

155*

5

100

12

14


0.50 to 1.00

90

340

-

-

13

15


0.50 to 1.00

70

340

-

-

14

16


1.00 to 1.50

110

210*

-

-

15

17

584.370, crack ,outer lane

0.50 to 1.00

85

345

-

-

16

18

584.505, transverse crack, inner lane

1.50

145

330

-

-

17

19

584.505, transverse joint, inner lane

-

Full depth

330

6

100

18

20


1.00 to 1.50

152

330

-

-

19

22


1.00 to 1.50

120

350

-

-

20

23

586.150 , crack, outer lane

2.50

Full depth

324

-

-

21

24


1.00 to 2.00

160

330

-

-

22

46


2.50

Full depth

345

-

-

23

47

587.750, tied shoulder

-

Crack induced

327

5

85

DISTRESSES I N CEMENT CONCRETE PAVEMENTS –A CASE STUDY

38

28


-

Crack not induced under

255

330

6

90

325

5

110

saw cut 39

30

622.190, transverse joint

-


saw cut 40

32


5.00 to 8.00

Full depth

340

-

-

41

31


-

Full depth

345

5

88

42

33

623.450, tied shoulder and transverse joint

-

Full depth

330

5

90

43

34


4.00 to 5.00

Full depth

345

-

-

44

35


-


340

4

95

saw cut 45

36


-

Full depth

340

5

95

46

38

624.560,crack, outer lane

0.50 to 1.00

120

325

-

-

47

39

624.560 , tied shoulder

-


330

5

105

saw cut

256 3.3

MISHRA, MATHUR , K UMAR UMAR , SENGUPTA AND GANVIR ON ANVIR ON Investigation of the Distresses Observed

Details of the various distresses observed in PQC have

been discussed below: Cracks 3.3.1 Longitudinal Cracks

The longitudinal cracks were the major distresses observed in total road stretch under investigation. cracks) 3.3.1.1 Chainage 586-588 (full depth cracks)

Longitudinal cracks extending to many slabs were observed at this section (Photo 9 & 10). In these stretch, continuous longitudinal cracks along with short length multiple parallel cracks were observed. Cracks were located in the middle one-third portion of outer lane of the concrete slabs. The width of the cracks was 2.5 mm. Cores No.23 and 46, when taken over the crack were recovered in four pieces showing full depth crack.

ing full depth crack.

Photo 10 Continuous Longitudinal Crack (Chainage 587.750) 3.3.1.2 Chainage 622-623 (full depth cracks)

Longitudinal cracks extending to many slabs were observed in outer lane at this section (Photo11). Cores were taken from the tied shoulder joints as well as from adjacent cracks to check the depth and possible causes of crack. Core No. 28 taken from tied shoulder joint shows that the joint had not induced under the saw cut.


Crack not induced under saw cut tied shoulder joint Crack Photo 11 Continuous longitudinal Cracks (Chainage 622.175) Full Depth

Full depth Crack

257


saw cut tied shoulder joint

Photo 12 Continuous Longitudinal Crack (Chainage 623.450) 3.3.1.3 Chainage 623-624 ( full depth cracks)

In this stretch of concrete pavement discrete continuous

3.3.1.4 Chainage 617.100 to 617.400 (full depth

258


of crack. The core taken over the crack propagated to 135 mm from the top of the slab. It was also observed that the tied shoulder joint had not gone to the full depth of PQC which is an indication of delayed sawing of joint. Width of crack is 0.5 -1.0 mm. A little bit spalling of crack’s edges was also observed at this location

Full Full Dept Depthh Cra Crack ck

Crack in induced un under sa saw cu cut tied shoulder joint Photo 13 Continuous Longitudinal Crack (Chainage 617.170)

The core no. 42 was taken over the crack. Examination of the core indicated that the crack had penetrated up to

Discrete Continuous Longitudinal Crack


has multiple parallel Y-shaped Y-shaped cracks (Photo 15).

259

260


depth crack that might have appeared before cutting of

the joints. Core No. 19 shows a saw cut transverse joint that had propagated full depth of the slab. Shrinkage

cracks were also observed in outer lane. Some of these transverse cracks were already been repaired by crossstitching.

Photo 18 Full width transverse crack in outer lane (Chainage 571.460) 3.3.3

Other Distresses

In addition to the longitudinal and transverse cracks, some other distresses were also observed and are discussed in the following sub sections.


261

attention as it is causing hindrance to vehicle movement

(Photo 21).

Photo 19 Corner Breaks

3.3.3.2 Pop out Pop outs have also been observed at some locations.

The diameter of pop out varies from 50 to 100 mm (Photo 20).

262


separation has been observed. The length is 18 m and width varies from 10 to 95 mm (Photo 24).

Photo 22 Scaling and repaired spalled joints 3.3.3.5 Partial depth 607.250)

repair

failure

(chainage

Badly deteriorated partial depth repair has been

DISTRESSES I N CEMENT CONCRETE PAVEMENTS –A CASE STUDY 4

DISCUSSION ON INVESTIGATION

263 THE

FIELD

The road stretch (340 mm thick) consists of two lanes with tied shoulders (1.5 M). The longitudinal cracks (full depth, partial depth) and multiple parallel longitudinal cracks were observed in the mid one-third of outer lane of concrete slab. The cores taken out from the cracked PQC slabs showed partial depth cracks as well as full depth cracks (cores recovered in pieces).

Photo 25 Joint Sealant Damage

in earthen shoulder 3.3.3.8 Rain-cuts gullies in

At various places, rain-cuts gullies in earthen shoulder have been observed. These might have occurred due to improper compaction of earthen shoulder that resulted

in washing out of the soil, due to rains (Photo 26).

Further, the cores taken from the adjacent tied shoulders showed that joint cuts had not induced under the saw cut inspite of adequate saw cut depth indicating delayed sawing operation for the joints. As per the records, routine maintenance of this road stretch has not been carried out since its construction

in 2004. The joint sealant in the longitudinal and transverse joints has either hardened or oozed out from the joints and at some places it is totally lost resulting in inltration of incompressible foreign material making

264


4.82% having crack width 2-3 mm & only 1.44% have cracks more than 3 mm. The main causes for the observed cracking and other distresses appeared

in the slabs are as below: Since the details of construction sequence and sawing of joints etc. at site were not available, location of the crack in the slabs revealed that the 8.5 m wide road (7 m plus 1.5 m, shoulder) was constructed in one go without sawing a longitudinal joint. Therefore, the stresses developed in the concrete slab (highest axle load stress plus temperature stress) might have exceeded the designed exural strength of concrete. The Y shaped shallow crack is due to plastic shrinkage that might have aggravated further by hot wind and poor curing conditions. The corner breaks at a few locations is due to locked joints i.e. poor load transfer and non-uniform support of` the slab at the corner.

The reason for the pop outs from concrete surface is the presence of the lump of clay or any soft /foreign

using cross stitching and sealing with epoxy resin. The same technique can be applied for the repair of other transverse cracks locations. Corner breaks occurred only at certain locations due to

the non-uniform support under PQC slab. Small pieces of concrete worn out from the surface of pavement due due to contamination of non durable material material

like clay lumps etc. were observed. These can be repaired with Epoxy mortar. Lane to medium separation caused at one location due

to the movement of the backll soil of the median is to be restored to avoid ingress of water and foreign material in the gap.

Damage of the joint seal at longitudinal and transverse joints needs resealing resealing and timely maintenance. It is suggested that the repairing of cracked slabs, with the techniques described in the following sections may be taken up in completely dry weather for best results. Procedure for carrying out various suggested repairing


as four slabs. These cracks are located in the middle 1/3 portion of the outer lane slabs. For repair purpose 1.0 to 1.5 m (as the case may be) portion of the slab has to be saw cut in such a way so that the total length of longitudinal crack is covered as shown in Fig. 1.

265

The lifting should be done as vertically as possible with minimum sway, since any deviation from this can damage the surrounding concrete.

When using mechanized breaking equipment like drop hammers or hydraulic rams, operators must exercise

control on the equipment’s break energy. Operators should begin breaking the concrete in the centre of

the removal area and move outward towards buffer cuts. Buffer cuts are made about 0.3 m away from the perimeter of saw cuts within the patch. The operator should reduce the break energy (drop height) before starting on the area outside the buffer cuts, then there

will be less chance of damaging concrete beyond the Fig. 1 Full Depth Repair for contionous Longitudinal Cracks with short length multiple parallel cracks (Spacing of Dowel & Tie Bars as per Design) Distressed Concrete Concrete 5.1.2 Removal of Distressed

Once the repair limits are saw-cut, the concrete is removed in two ways. One is the lift out of the

patch perimeter. perimeter.

If sub-base has been damaged during removal operation of old concrete then it would be necessary to repair it by adding and compacting compacting new sub-base material.

266


nozzle that feeds the epoxy to the back of the hole.

Insert new dowel bars accurately aligned parallel to the surface and sides of the slab. Make sure that the

epoxy anchoring material ow forward along the entire dowel embedment length during insertion. De-bond the dowel bars with thin, tight tting plastic sheaths. A bond breaking 5-6 mm thick bre board should be placed along any longitudinal face with an existing concrete to move independently. Tie bars should shoul d be b e place p laced d at a t the th e locat l ocation ion of longit udinal udina l

joints joint s when the t he patch pat ch area are a involves invo lves all a ll the lanes. la nes. The Th e length, diameter, and spacing of dowel and tie bars may be the same as used during the construction of the pavement. 5.1.4 Placing and Finishing Finishing the New Concrete Concrete

Place and evenly spread pavement quality concrete of

M40 Grade to the appropriate surcharge. Thoroughly compact the concrete using internal vibrators and then

nish the surface with the help of a screed vibrator.

Preparation for laying of concrete in distressed portion


no de-lamination, the sound will be solid. On the other hand a dull or hollow sound indicates the probability of de-lamination.

267

Cross-stitching uses deformed tie bars drilled across a crack at angles of 30-45 degrees (Photo 30). Deformed steel bars of 16 mm diameter are sufcient to hold the crack tightly closed and enhance aggregate interlock.

5.2.2 Remove Deteriorated Concrete Concrete

After the repair limits are determined, the delaminated concrete should be removed. A typical method for

removing spalled concrete is chipping. A shallow vertical saw-cut, approximately to the depth of spall, made around the perimeter of the spalled area can be used to prevent the tapering of the repair around the

perimeter. Chipping is done with light pneumatic tools. 5.2.3

Full depth holes of 18-20 mm dia. are drilled at a pitch distance of 300 mm with the offset of 150 mm from the crack. The holes are drilled alternately from each side of the crack so that one hole passes through the crack

from left to right while the next from right to left. After drilling, the holes are ushed with high pressure air to clean out any residual dust. Then a high strength epoxy resin adhesive is injected into the holes. Immediately after injecting epoxy, deformed steel rods are inserted into each hole.

Clean the Repair Surfaces

For Partial Depth Repair to succeed, good bonding between the exposed concrete surface and repair material is essential. It is important to expose a fresh concrete surface. This should have rough texture and be cleaned with water to remove any dust. dust.

MISHRA, MATHUR , K UMAR UMAR , SENGUPTA AND GANVIR ON ANVIR ON DISTRESSES I N CEMENT CONCRETE PAVEMENTS –A CASE STUDY

268

saw. Concrete saw can be used to make shallow tine grooves. A single blade can be used for this purpose but alternatively a couple of blades can be assembled

with spacers so that in one pass a couple of grooves can be formed. The joint cutting machine may m ay have to be modied to have this arrangement. 5.8

Joint Resealing

It is generally considered a maintenance activity, but may also be done in conjunction with other restoration techniques for rehabilitation purposes. The process involves removing the old sealant, if present, sawing a new joint reservoir of appropriate dimensions for the sealant to be used, thorough cleaning of the new reservoir and installing the sealant. Material used for

joint resealing includes rubberized asphalt, silicone, and preformed neoprene inserts. When done as part of a restoration effort, joint resealing should be done after all other treatments, e.g., full-depth repair, partial-depth repair, under sealing, load transfer restoration and/or

intrusion of incompressible materials in the joints are adding to the problem. Remedial measures have been suggested in the paper for various distresses and should be executed at the earliest to strengthen the distressed pavement and to prevent further deterioration. The remedial measures suggested are based on the practical viability and economy. Acknowledgements

Authors thank NHAI for sponsoring the Project. Authors also thank Shri Pankaj Goel, Shri Manoj Kumar Singh and Shri Ashok Pant for assistance

provided during eld investigations. investigations. The authors are grateful to Director, Central Road Research Institute for the permission to publish the paper. REFERENCES

1.

Jointed Plain Cement Concrete (JPCP), Preservation & Rehabilitation, Design Guide,

Paper No. 601

REHABILITATION REHABILITATION AND UPGRADATION UPGRADATION OF AN EXISTING EXISTIN G AIRFIELD RUNWAY PAVEMENT FOR OPERATION OF NEXT GENERATION GENERATION AIRCRAFTS AIRCRAF TS R AHUL AHUL OBEROI*AND A. VEERARAGAVAN** ABSTRACT With the introduction of heavier aircrafts in the Indian ai r force and the rapid expansion of airelds, there is a need to bring out more cost effective designs of aireld pavements and to apply the concept of the overall lowest life cycle cost as opposed to initial lowest cost. The current design methodology for airelds in the armed forces in India is restricted to the Federal Aviation Administration (FAA) method of aireld design as outlined in International Civil Aviation Aviation Organisation (ICAO) Aerodrome Design Manual Part 3, Pavements. However, these methods can no longer be c onsidered onside red to result in optimal optim al thickness thick ness of pa vement layers layer s and a nd there t here is therefore there fore a ne ed t o design de sign the runway pavements paveme nts using mechanisti mecha nisticcempirical pavement design methods as per International best practices. In the present investigation, the rehabilitation and upgradation of an in-service air force runwayis considered. The existing runway pavement has developed extensive distresses due to inadequate surface and sub-surface drainage and operations. The rehabilitation of the runway to cater to the needs of the present as well as the future new generation aircrafts has been carried out. The present work addresses the pavement and overlay design of the airel d runway pavement. The runway was designed as per the FAA and ICAO methods. APSDS (Airport Pavement Structural Design System) software with its parametric analysis feature for layer optimisation was found to be the most suitable software for obtaining economical designs for runway pavements. Life cycle cost anal ysis was carried out to dete rmine the most economical bi nder for the wearing course for the runway pavements and i t was found that the use of modied binders in Dense Asphalt Concrete (DAC) surface course resulted in signicant savings in the life cyclecost of overlays

270

OBEROI AND VEERARAGAVAN ON designs an d selection of the cost-effective design for the desired performance during the design life.

being inducted in the air force, this old methods can no longer be considered optimal and there is therefore

a requirement to design runways as per new elastic layered theory design software like FAARFIELD, APSDS, Asphalt Institute’s SW-1 software, etc. and draw comparisons with the ICAO method. There is also a requirement to realistically evaluate the

existing runways and assign moduli values to the constituent layers for economical designs using these

software rather than continuing to assign equivalence factors to the constituent layers which may lead to erroneous results. The present study attempts to draw comparisons between the various design methods both

4

SCOPE

The aireld selected for rehabilitation and upgradation shows signs of functional distresses like network of shallow, shallow, ne hair line cracks which extend through the upper surface of the black top. Due to an increase in

the anticipated trafc including introduction of heavier aircraft and rapid deterioration of the aireld, there is a need felt for strengthening and upgradation of the

analysis so as to achieve the most economical design

aireld pavements and construction of a new surface for improved performance. The present work will address the design needs of the runway for the operation of next

over the design life of the runway pavement.

generation air force aircrafts.

The study has practical applications, especially for the armed forces who are involved in construction of airelds in high altitude and far ung areas where

5

LITERATURE REVIEW

5.1

Evaluation of Aireld Pavements

for rehabilitation and upgradation of an existing air

force runway pavement considering the life cycle cost

R EHABILITATION EHABILITATION A ND UPGRADATION OF A N EXISTING AIRFIELD R UNWAY UNWAY PAVEMENT FOR O OPERATION OF NEXT GENERATION AIRCRAFTS

on National Airport Pavement Test Facility (NAPTF) at New Jersey. They concluded that the pavement stiffness and back-calculated subgrade moduli values are independent of FWD/HWD force amplitudes. They also concluded that the relationship, E (psi) = 1500 x California Bearing Ratio (CBR) used in design software is reasonable when applied to the subgrade modulus (E) back-calculated from FWD/HWD data in the range 3
increased as a result of trafcking. 5.2

Trends in Flexible Pavement Design

The conventional empirical methods for structural design of exible aircraft pavements are now recognised to be inadequate to assess the effect of proposed new

271

of pavement reconstruction. WHPACIFIC, INC (2010) used FAARFIELD and made use of cores and test pit data to design an overlay for Grants Pass Airport 12-30 Runway. Runway. Both overlay option for in-situ CBR of 2 and full depth reconstruction option with an improved CBR of 5 were considered. In the absence of an alternate aireld and considerable time required for the full depth reconstruction option, the overlay option was recommended.

White (2006) studied the equivalence factors of different pavement layer materials as recommended

by FAA and proposed that for drawing comparisons with thicknesses derived by APSDS Software, the equivalence factors should lie at the lower end of the FAA range. White and McCullagh (2006) demonstrated the use of APSDS and FAARFIELD softwares for upgradation of an Australian defence aireld which resulted in considerable savings in time and cost. 5.3

Use of Modied Asphalt Mixes

272

OBEROI AND VEERARAGAVAN ON

performance models with the traditional distress base. Besides the above, aireld pavement design software have inherent performance parameters which can predict pavement performance with age. age. From the above literature review, it is observed that a number of methods exist for design, rehabilitation and

upgradation of airelds. However, a comprehensive study which compares various aireld pavement design methods to include aspects of life cycle cost analysis is

needed which this study attempts to achieve. 6

METHODOLOGY

study:

Review

of

literature

regarding

aireld

pavements, evaluation techniques, design of

Life cycle cost analysis and selection of optimal layer design including incorporation of

modied bitumen binders. 7

DESCRIPTION OF THE AIRFIELD

The aireld under consideration is an air force aireld located in coastal South India and has two intersecting runways with different congurations. The orientation of the main runway is 12-30 while that of the secondary runway is 05-23. A brief description of these runways is given below : 7.1

The following methodology was adopted for the a)

e)

Main Runway 12-30

The main runway is a exible pavement, 1784 m long, 45.72 m wide and consists of the following sections: a)

Section 1 – 50 DAC (constructed in 2003), 200 BM, 150 Soling (constructed in 1944) and CBR 3%.

b)

Section 2

exible runway pavements and overlays and life cycle cost analysis.

50 DAC (constructed in 2003),


The same information is pictorially represented in Figs. 1(a) and 1(b):

Table 1 Predicted Air Trafc Data No. Na Name*

7.3

Gross Wt. (tonnes)

Gear Annual Conguration Departures

Total Departures

1

AN 32 27.000 (Dual Whl-60)

Dual

3,000

60000

2

(Single 1.322 Wheel1500 kg)

Single

10,000

200000

3


Single

3,500

70000

4


Single

5,000

100000

Fig. 1(a) Composition of Main Runway

Fig. 1(b) Composition of Secondary Runway

273

*Some aircraft names withheld due to being classied information

Pavement Condition 7.5

The Soil Engineering and Material Testing (SEMT) Wing of the Corps of Engineers carried out evaluation of the aireld in Aug 2008 and concluded that the

Introduction of New Large Aircraft

For the purpose of this study, a hypothetical case of the introduction of C 17 aircraft has been considered

274


samples. Fig. 2 depicts the present condition of the aireld:

thickness and moduli value of the various pavement

layers in conjunction with other input parameters like temperature and air trafc to compute the layer or overlay thickness, repetitions to failure, residual

life and so on for the safe operation of the new large aircraft. The following methods have been used for the purpose of this study: study:

a)

The United States of America Federal Aviation Administration method as given in ICAO Aerodrome Design Manual Part 3 Pavements

(1983) hereafter referred to as the FAA manual manual method of design.

b)

The automated method of FAA using FAARFIELD software.

c)

APSDS software for aireld pavement design.

d)

Asphalt Institute’s Institute ’s SW-1 software. software .

The pavement design was done in two stages for all


275

bases P-401/P-403 (Equivalent of DAC/DBM) as 2758 MPa. Modulus value of BM has been taken as 0.7 x Modulus of DBM as per IRC 37-2001 = 0.7 x 2758 = 1930 MPa.

and proposed layers is shown in Table 2: Table 2 Layer Equivalencies Type of Layer

Base Course Equivalence

Sub-base Course Equivalence

Existing DAC

1.5

2.3

Proposed DAC/DBM

1.6

2.3

Brabston base/sub-base respectively and their

Existing BM

1.2

2.0

modulus value is calculated automatically by

NA

1.4

PCC/WBM/WMM/

c)

Base/Subbase layers : The WMM and GSB courses have been considered as Barker

the software.

Soling

8.6 8.3

Determination of Design Aircraft

Aircraft Wander

3243. For the hypothetical trafc, C 17 was determined

A normally distributed airplane wander pattern with a wander width of 1800 mm and a standard deviation of 773 mm has been used (equivalent to an airplane operation on a taxiway). The values are based on studies carried out by H o Sang, (1975). Field survey and

to be the critical aircraft and the total annual repetitions of the design aircraft for the predicted hypothetical

analysis of aircraft distribution on airport pavements,

Report No. FAA-RD-74-36. U.S. Federal Aviation

trafc amounted to 613. Calculations are shown in

Administration.

For the predicted trafc mix, AN 32 was determined to be the critical aircraft and the total annual annual repetitions repetitions of the design aircraft for the predicted trafc am ounted to

Appendix 1

276


the users to either dene their own layers with

value of both 1379 MPa and 2758 MPa for comparison

their performance parameters or choose from

purposes.

the inbuilt database. However, for the purpose of comparison with FAA methods, the existing

8.10

HMA layer has been assigned moduli values of

2758 MPa and 1379 MPa. b)

Existing Bituminous layers layers : Modulus value of bitumen stabilised bases DAC/DBM has been assigned as 2758 MPa similar to FAARFIELD. Similarly, Similarly, modulus value of BM has been taken

1930 MPa. c)

Aircraft Wander

APSDS offers exibility to the user to dene aircraft wander for any trafc spectrum. The standard deviation for aircraft wander for this study is 773 mm and a wander width of 1800 mm. 8.11

Performance Criteria for Subgrade Failure and Bituminous Layer Failure

Base/Subbase layers : The WMM and GSB courses have been considered as Barker Brabston base/sub-base respectively.

Vertical strain at a t the top of the subgrade subgra de and horizontal strain at the bottom of the top layer are the design

layer (WMM) in carrying out designs with both FAARFIELD and APSDS. Table 3 shows the moduli

criteria for the pavement. Users can dene their own performa perf ormance nce param p arameter eterss and there is more mo re exibi  exibility lity than FAARFIELD. In drawing comparisons in thickness design, FAARFIELD subgrade damage

values assigned to the various existing and proposed

paramete para meters rs have also been fed in APSDS AP SDS for design desig n

layers in both the software:

calculations. However, the asphalt layer damage

The PCC layer in Section 3 of the main runway has been considered considered to be be equivalent equivalent of a crushed aggregate


Main Runway

277

140

93

8 3 .9

80.21

70.59

79.76

6 9 .7 9

2 10

183.9

177.2

170.35

164.20

169.96

164.44

535

618.5

600.2

444.85

430.81

563.46

546.52

20 5

1 7 3 .1

166.7

159.85

153.77

159.44

153.86

Section 3

Main Runway Section 4 and

PTT 12-30 Main Runway Section 4 with C 17 Aircraft

Secondary

Runway and PTT 05-23 Extension

Portion with existing eet Extension

Portion with C-17 and AN 32 8.13

DAC-50 DBM-100 WMM-255 GSB-250 DAC-50 DBM-225 WMM-590 GSB-250

DAC-50 DBM-100 WMM-299 GSB-250 DAC-127 DBM-150 WMM-763.2 GSB-250

Analysis of Results

From the results above, it is observed that signicant variation in thickness occurs depending on the failure

criteria used (Refer Appendix 2) and the modulus

DAC-50 DBM-100 WMM-290.93 GSB-250 DAC-125 DBM-150 WMM-581.17 GSB-250

DAC-50 DBM-100 WMM-274.52 GSB-250 DAC-50 DBM-225 WMM-704.57 GSB-250

seven were used for calculation of various parameters and moduli values as shown in Tables 5 and 6. Table 5 Summary of Test Results of Bituminous Samples

278

OBEROI AND VEERARAGAVAN ON Table 6 Laboratory Obtained Dynamic Modulus Values Values of Bituminous Samples in MPa at 350C

Frequency (Hz)->

25

20

10

5

2

1

0.5

0.2

0.1

0.01

Sample Type

BM 1

4580

433 7

357 7

2917

2170

1705

1326

935

71 8

301

BM 2

4443

4245

3495

2818

2061

1594

1225

862

664

293

BM 3

4 001

3762

3062

2462

1795

1394

10 67

740

562

237

BM 4

3830

3633

2961

2373

172 0

131 8

100 1

687

510

202

BC 1

457 7

4290

3356

2569

173 8

1271

936

642

494

254

BC 2

4334

4 046

3 140

2375

1586

1147

840

576

438

224

BC 3

3261

3046

2324

1716

1112

790

580

400

3 17

1 78

BC 2 VG 30#

4525

4118

3344

2673

1918

1454

1101

7 61

5 82

27 1

BMB*

6128

588 3

5143

4468

3661

3137

2680

216 0

183 7

104 2

CRMB*

5358

5144

4461

3859

3151

2 683

2 298

1868

1604

933

* Tests carried out at IIT Madras

R EHABILITATION EHABILITATION A ND UPGRADATION OF A N EXISTING AIRFIELD R UNWAY UNWAY PAVEMENT FOR O OPERATION OF NEXT GENERATION AIRCRAFTS Table 7 Comparison of Final Layer Thicknesses by Various Methods Runway Section

Main Runway

Overlay / New Layer Thickness with FAA Manual Method (mm)

Overlay / New Layer Thickness with FAARFIELD (mm)

Overlay / New Layer Thickness with APSDS (mm)

130

110

100

100

110

100

279

Table 8 Subgrade Compaction Requirements For Existing Trafc

Compaction density, in percentage Depth, mm

100%

-

95%

90%

85 %

80 %

0-150

150300

300480

480-635

Section 1

Main Runway Section 2

Main Runway

For Trafc with C17 Aircraft

Depth, mm

140

1 20

110

210

2 00

190

-

0-23

23-46 46-69

69-92

Section 3

Main Runway Section 4 and

PTT 12-30 Main Runway Section 4 with

535

6 40

580

205

1 90

180

C 17 Aircraft

Secondary

8.20

Parametric Analysis with APSDS Software

In APSDS Software, Parametric Ana lysis feature can loop through a range of thicknesses for one or two layers, while simultaneously designing the thickness of another layer. Combining this with a Cost Analysis feature, allows for e-tuning of layer thicknesses

280 8.21

OBEROI AND VEERARAGAVAN ON Parametric Analysis

As per FAA AC 150-5320-6E, the minimum stabilised base thickness is 127 mm. The remaining base can ca n be unstabilised unstabi lised bas e. Hence the th e independent indepe ndent

layer for parametric analysis is the WMM layer with a minimum thickness of 400 mm and a maximum thickness of 700 mm. The DBM layer has to be designed. The minimum thickness of the DBM layer has been set as 127 mm and maximum as 200 mm. The cost of the constituent layers has been bee n taken from the schedule of rates, Govt. of Karnataka, 2010. 8.22

4.

WMM NA (BB) (P-209)

610

Unstabilised Base

5.

GSB (BB) (P-154)

250

Subbase

6.

Subgrade CBR 31

NA

0

03

Discussion of Parametric Analysis

From Fig. 3, it is seen that the minimum total cost is when the thickness of the WMM layer is 620 mm. At this juncture, it is seen from Fig. 5 that the thickness of the DBM layer is 127 mm (5 inches), the t he minimum thickness allowable allowa ble for this layer. It is also seen from Figs. 3 and 4 that increasing the thickness

Fig. 3 Variation of Total Cost with WMM Layer Thickness


Asphalt Institute and is based on mechanistic-empirical principles of Asphalt Institute. Full depth asphalt pavements and overlays can be designed by SW-1. Moduli values of various layers are assigned based on

AI criteria and are temperature dependent. 8.24

Unlike APSDS, SW-1 does not have the exibility of enabling the user to dene any aircraft. It is for this reason that a trial air trafc trafc has been considered for

design. Only those airplanes that are available in SW-1 as well as FAARFIELD and APSDS are considered, so that comparisons can be drawn. In this section, a new full depth asphalt pavement is designed for the predicted air trafc shown in Table 11 for a period of 20 years. Table 11 Predicted Air Trafc for Design Comparison with SW-1 Software Weight in

Analysis of Results

From the results above, it is observed that APSDS software presents the most economical amongst all design methods discussed. It is also seen that FAA manual method is not economical owing to full depth asphalt pavements.

Air Trafc

Aircraft

8.26

281

Annual

Total

Gear

9

LIFE CYCLE COST ANALYSIS

Life-cycle cost analysis (LCCA) applies the discount rate to the life-cycle costs of two or more alternatives to accomplish a given project or objective, enabling the least cost alternative to be identied. LCCA enables the analyst to make sure that the selection of a design

alternative is not based solely on the lowest initial costs, but also considers all the future costs (appropriately discounted) over the project’s usable life. Present worth or present value economic analyses are considered to be the best methods for evaluating airport pavement design or rehabilitation alternatives. A discount discount rate of

4 percent is suggested together with an analysis period

282


of DAC with VG 30 has been replaced by layers of modied binders to study the effect of increase in structural life with the use of modied binders. The modulus value of the top DAC layer has been xed at 1379 MPa as per FAA AC 150-5320-6E, 2009. The experimental value of the DAC obtained

Table 14 Time for Reaching CDF 0.2 with Different Binders Top Layer L ayer Modulus Time to Total DAC (MPa) Reach CDF Aircraft Binder 0.2 (Years) Repetitions

Remarks

Extension Portions for C 17

in the laboratory at 35 0C and 5 Hz frequency

VG 30

13 79

3.94

1970

was found to be 2500 MPa. The moduli value of 1379 MPa works out to be 55% of the experimental

Rounded up to 4 years

CRMB-55

2123

7.56

37 80

Rounded up

value. Hence the moduli value of the DAC layers

with modied binders has also been xed at 55% of the experimental value obtained. The modied

to 7 years PMB (SBS)

2165

7.96

39 80

Rounded up

to 8 years Main Runway Section 4 for C 17

binde rs used and the corresponding correspo nding dynami c modulus modu lus 0 values of DAC using these binders at 35 C and 5 Hz

VG 30

13 79

3.96

1980


frequency are shown in Table 13 below.

CRMB-55

2123

9.04

45 20


PMB (SBS)

2165

9.74

48 70

Table 13 Modied Binders Considered with Corresponding Modulus Values Binder Used

Modulus Value Modulus Value Remarks of layer at of Top Layer 350C and 5 Hz using Modied (MPa) Binder

Rounded up

to 10 years Extension Portions for AN 32

VG 30

13 79

3.93

11800


CRMB-55

2123

75

22500

Rounded up


The initial construction costs have been calculated for extension portions for C17 aircraft and also for AN 32 aircraft. Th e overlay costs have been calculated for both the extension portions as well as for Section 4 of the main runway which is the most critical. For calculation purposes, the overlay thickness has been restricted to 50 mm, the minimum thickness stipulated by FAA AC 150-5320-6E as the binder is being varied in only the top 50 mm portio por tionn of the overla ove rlay. y. The T he timing tim ing for the overla ove rlays ys has been calculated based on the CDF of 0.2. All costs have been converted to the net present value considering a discount rate of 4 percent. Routine maintenance costs have not been conside red as they have been assumed to be the same for all type of binder bin ders. s. Also, Als o, for the purpos pur posee of this thi s analys ana lysis, is, no

major rehabilitation has been considered. The 20 th year marks the end of the analysis period. Only the salvage value of the overlay has been considered, all other factors being the same. Summary of Alternatives Table 16 shows the summary

9.6

283

Analysis of Life Cycle Cost

From Table Table 15, it is seen that although the lowest initial cost of construction is obtained by using VG 30, the lowest life cycle cost is obtained by using CRMB-55 in the top 50 mm of DAC. Further, even though the cost of DAC with PMB (SBS) is almost 30% higher than DAC with VG 30, the life cycle cost for overlays using PMB works out to be almost 40% lesser than overlays using VG 30. The use of CRMB-55 for overlays results in a saving of 50%. Another important factor which should be considered here is that owing to the lower frequency of overlays using modied binders, there will be reduced closure of the aireld for maintenance which will result in further savings. 9.7

Performance of Different Binders at Higher Temperatures

Though LCCA was carried out at a temperature of 350C, the actual pavement temperature often exceeds

284

OBEROI AND VEERARAGAVAN ON Table 18 Time for Reaching CDF 0.2 with Different Binders

Top Layer L ayer DAC Binder

Modulus (MPa)

Time to Reach CDF 0.2 (Years)

Total Aircraft Repetitions

Remarks

b)

failure criteria used and the modulus values

adopted for bituminous mixes. Signicant variation also occurs due to the equivalency factors assigned to the existing materials in the manual method. Hence, the modulus values and equivalency values need to be assigned carefully after laboratory testing.


VG 30

67 5

2.12

1060


CRMB-55

1060

3.02

1510


PMB

1492

4.34

2170


(SBS)

c)

Table 19 Life Cycle Cost Comparison of Alternatives at 450 Celsius Top Layer L ayer Binder

Initial Cost 2

(Rs/m )

Present Worth Life Cycle Cost (Rs/m2)


VG 30

2927

5320

The variation in thickness depends on the

From laboratory experiments, the moduli values of the constituent DAC and BM layers were found to be 2500 MPa. These were however restricted to 1379 MPa for the top layer of DAC as per latest FAA guidelines and 1250 MPa for BM to account for the considerable ageing and

deterioration due to water inltration. d)

It was observed that the FAA manual method of design is uneconomical for overlays for light

aircraft while it is economical for overlays with heavy aircraft and new designs. FAARFIELD, on the other hand results in thicker overlays as

R EHABILITATION EHABILITATION A ND UPGRADATION OF A N EXISTING AIRFIELD R UNWAY UNWAY PAVEMENT FOR O OPERATION OF NEXT GENERATION AIRCRAFTS REFERENCES

1.

285

11.

Federal Aviation Administration (FAA), Advisory Circular 150/5335-5A, (2006), “Standardized Method Of Reporting Airport Pavement Strength – PCN.”

12.

Federal Aviation Administration (FAA), Advisory Circular 150/5320-6E, (2009).

Asphalt

Institute, MS 11, (1987). “Thickness Design - Asphalt Pavements for Air Carrier

Airports.”

Asphalt Institute, SW-1 Software. “Asphalt Pavement Thickness Design Software for Highways, Airports, Heavy Wheel Loads and Other Applications, (2010).”

13.

Federal Aviation Administration (FAA), FAARFIELD Software, Version 1.302 (2009).

3.

Bentley Systems, System s, MX ROAD Software, Version Version v8i (2010).

14.

Federal Aviation Administration (FAA), COMFAA Software, Version 3 (2010)

4.

Chen, Ye Sun and Zummo, Guy. (2003).

15.

Gendreau and Soriano. (1997). “Airport

2.

“Pavement

Design

to

Accommodate

the

“Airport Pavement Design and Evaluation.”

Pavement Management Systems: An Appraisal

Airbus A380 at John F. Kennedy International Airport.” 83rd Transportation Research Board Annual MeetingWashington, D.C. 5.

Dhaliwal, B.S. and Tipnis M.M. (2004). “Planning for Rehabilitation of a Disused

of Existing Methodologies.” Pergamon, Transpn Res.-A, Vol. 32, No. 3, pp.197-214, 1998. 16.

Greene, J., Shahin, M. and Alexander, D.

(2004). “Aireld Condition Assessment.” Transportation Research Board Annual

286


23.

Kasthurirangan Gopalakrishnan, (2008). “Forensic Investigation of Failed Aireld Test Pavements.” KSCE Journal of Civil Engineering (2010) 14(3) :395-402.

24.

McQueen ,R.D., Wayne Marsey and Jose M. Arze, (2001). “Analysis of Non Destructive Test Data on Flexible Pavements Acquired at the National Airport Pavement Test Facility.” Federal Aviation Administration Airport Technology Research and Development

31.

Veerar agavan agavan and Shailendra Grover. (2008). “Forensic Investigations of Pavement PreMature Failure of a National Highway Pavement due to Poor Sub-Surface Drainage.”

32.

Wardle, L. and Rodway, B. (1998). “Recent Developments In Flexible Aircraft Pavement Design Using The Layered Elastic Method.” Third International Conference on Road and Aireld Pavement Technology, Beijing, April 1998.

33.

Wardle, L. and Rodway, B. (2010). “Advanced Design of Flexible Aircraft Pavements.” 24 th

Branch. 25.

Mincad Systems, Airport Pavement Structural

Design System (APSDS) Software, Version4 (2006). 26.

Norlela Ismail, Ismail, Amiruddin Ismail and and Riza Atiq O.K. Rahmat. (2009). “Development of Expert System for Airport Pavement Maintenance and

Rehabilitation.” European Journal of Scientic Research ISSN 1450-216X Vol.35 No.1 (2009),

ARRB Conference, Melbourne, Australia. Australia. 34.

White G.W. and McCullagh P.J. (2006), “Upgrade of an Australian Defense Aireld for the Introduction of Code E Aircraft.” Proccedings of the 2006 Aireld and Highway Pavement Speciality Conference.


287

APPENDIX 1 DETERMINATION OF DESIGN AIRCRAFT Table 1 of Appendix 1–Equivalent Annual Repetitions of Design Aircraft AN AN 32 Aircraft

Wt in Kg

Repetitions

Wheel Load

Design Aircraft Repetitions*

Equivalent Annual Repetitions#

Gear

AN 32

27000

3000

6412.5

3000

3000

D

(Single Wheel4500 kg)

4600

3500

2185

2800

103

S


4536

5000

2154.6

4000

123

S


1322

10000

627.95

8000

17

S

Total

3243

*For conversion of Single wheel (S) repetitions to Dual Wheel (D) repetitions, depatures of S to be multiplied by 0.8 (Single wheel to dual wheel factor) #For conversion to equivalent annual departures of design aircraft, use Eq. 5.1, log R 1= log R 2 x (W2/W1)1/2 ...5.1

288

OBEROI AND VEERARAGAVAN ON R EHABILITATION EHABILITATION A ND UPGRADATION OF A N EXISTING AIRFIELD R UNWAY UNWAY PAVEMENT FOR O OPERATION OF NEXT GENERATION AIRCRAFTS APPENDIX 2

Performance Criteria for Subgrade Failure and Bituminous Layer Failure: FAARFIED

Performance Criteria for Subgrade Failure and Bituminous Layer Failure : APSDS

The design process for exible pavements considers two modes of failure: vertical strain in

Vertical strain at the top of the subgrade and

the subgrade and horizontal strain in the asphalt layer. Limiting vertical strain in the subgrade is intended to preclude failure by subgrade rutting. Limiting horizontal strain at the bottom of the asphalt surfacing layer guards against pavement failure initiated by cracking of the asphalt surface layer. Subgrade vertical strain and horizontal strain at the bottom of the top layer are the design criteria

horizontal strain at the bottom of the top layer are the design criteria for the pavement. Most of the models in APSDS are represented in the form of Eq. 3. C=k/Є]b

...3

Where, C is the predicted life (repetitions)

for the pavement. The failure model used to nd

k is a material constant

the number of coverages to failure for a given vertical strain at the top of the subgrade is given in Eq. 1.

b is the damage exponent of the material

Є is the induced strain (dimensionless strain) Log-log relationships can be readily converted to

Paper No. 602

CASE STUDY ON NEW INITIATIVES TAKEN ON CAISSON FOUNDATIONS FOUNDATIONS AND CUTTING CUTTI NG EDGE EDG E CONSTRUCTION CONST RUCTION AT AT BOGIBEEL BRIDGE A NUPAM NUPAM DAS* ABSTRACT Time is the essence of construction. Bridging the mighty & ferocious river Brahmaputra Brahmaputra is a great challenge in itself. In this paper, the engineering engineering solutions are presented which are derived by adopting revised & innovative methodology, for the construction of two difcult Caisson foundations namely P2 & P3 in River Brahmaputra at a Water depth of 14m to 18m, under water velocity ranging from 3 to 5m/sec, within very short period of 4 months (from November to February) February) only. only. After After adopting the revised revised methodology, methodology, both the Caissons were successfully grounded only in 74 days and a time of 53 days was saved in comparison to earlier season. The fabrication/ erection of each cutting edge at location was achieved in 10 days and a time of 15 days was saved in comparison to earlier season. This paper would immensely be benecial for Highway Engineers, as it involves substantial reduction of time of execution by 42% for caisson foundation & by 60% for fabrication & erection of cutting edge at location.

1

INTRODUCTION

The Bogibeel Bridge is the fourth bridge across river Brahmaputra, approximately 17 km

rail-cum-road bridge in India having total length of 4.94 km. 2 DESCRIPTION DESCRIPT ION OF THE PROJECT

290

DAS ON

October and again the water level and velocity starts increasing from March onwards. Scope of work includes, 42 nos. of double ‘D’ (16.2 m X 10.5 m) well foundations of 58.6 m depth for P2 to P39, 68.75 m depth for P1 and P40 and 42.00 m depth

in the upper reaches of the river. The fact is, working on a river Brahmaputra, one cannot follow a strict methodology. The river takes a new form/

rains

changes its course every year – the depth, bed level situation etc. changes leading to forced change in the

involved is 3,43,424 cum. Caisson foundations are,

planned methodology. The Working season is hardly, ha rdly, four months i.e. Nov. to Feb., as workable water level recedes by end of Oct. and Starts rising from 1 st week

one of the most difcult deep foundations to construct

of March itself.

for A1 and A2, including 3nos . of Caisson found ations

along with Pier and Pier Caps. The total Concrete

in bridges and that, building them in mighty and ferocious River Brahmaputra is itself a great challenge.

More challenge was added on, by the sudden ash oods due to untimel y and unprecedented heavy

In the following paras methodology adopted for the construction of well caisson during working season (2009-10) is presented:

NITIATIVES TAKEN O N CAISSON FOUNDATIONS A ND CUTTING EDGE CONSTRUCTION CASE STUDY O N NEW I NITIATIVES AT BOGIBEEL BRIDGE

291

Fig. 3 Dredging of River for Shifting of Caisson

The caissons (i.e. P2 / P3) were taken to the actual location on 17/01/2010 and 21/01/2010 respectively, after dredging and making the channel (Refer Fig. 4).

DAS ON

292

and slowly the P2 caisson submerged into water (Refer Fig. 7).

Fig. 5 Unprecedented ood in river Brahmaputra

Two of the three anchors of P2 caisson gave way due to heavy wind and water current. The caisson P2 gradually drifted and stabilized at about 130 m downstream side from the original location (Refer Fig. 6).

Fig. 7 P2 Caisson submerged in river Also at location P3, due to unexpected rise of water level


Before snapping of the tethering arrangements

the status of both the caissons were as follows (Refer Table 1). Table 1 Status of Caisson P2 & P3 Before Snapping of Tethering Arrangements S. No.

Description

1

Height of the Caisson

2

Weight of structural Weight of of

3

Unit

Caisson P2

Caisson P3

M

18.7

13.9

MT MT

138 77

117 77

MT MT

96 0 1175

315

9.7 9.0

5.6

293

ISA 90x90x8 at 1374 mm c/c at well curb portion of steel caisson was an important aspect to be checked. 3.1.1.1 Check for vertical frame during oating condition

Maximum water head/ Static Water pressure on the curb portion was considered to be around 7.50 7.50 m along with Water current of 3 to 5 m/sec. The pressure due to water current was then evaluated. Concrete pressure during concreting of well curb was also evaluated. Therefore, considering maximum of the two, the Design pressure was considered.

reinforcement 4 5

Weight of concrete Total weight of

5 09

caisson 6

Draft

M

7

Free board

M

8.3

To conclude, both the caissons were lost due to: (i)

Late grounding of Caissons, due to the delay of

i)

External Plate

Thickness of the plate was considered to be 8mm. Considering the maximum size of the panel, Bending

stress, Deection, was evaluated and checked with permissible values.

ii)

Vertical Angle

DAS ON

294

velocity =5 m/s (assumed during lwl condition) & pressure due to water current. Based on this, the no. of tethering arrangement, force in each wire rope & force in inclined wire rope were evaluated. 3.1.2.2 Wind Force It was Calculated, considering the basic wind speed =50 m/sec, designed wind velocity & pressure due to water velocity. Based on this, no. of tethering arrangement, force on each wire rope, force on inclined wire rope was evaluated.

Fig. b Fig. 9 (a & b) Structural details of Caisson

From the above, it wa s concluded that, the vertical frame angle ISA 90x90x8 @ 1374 mm c/c was safe in oating condition / sinking as land based well, due to proper bracing with other vertical frames as well as planned bracing at appropriate spacing (Refer Fig. F ig. 9 a & b).

Subsequently the total force on each Wire rope and its design force were evaluated. 3.1.2.3 Design 3.1.2.3 Design of Wire Wire Rope

(a)

the breaking load and factor of safety. safety.

(b) 3.1.2

Review of Design of Tethering Arrangement

Main wire rope force was checked, with steel core wire rope as per IS:2266:2002, considering Force from three sheave pulley to double sheave pulley, pulley, was checked considering the force, no.


295

Revised tethering arrangement by using 52 mm dia wire rope in place of 32 mm dia wire rope and 40 mm dia wire rope in place of 25 mm dia wire rope are shown in Fig.11. Fixing of winches from ground anchors are shown in Fig. 12.

Fig. a

Fig.11 Revised tethering arrangement of Caisson

Fig. b

296

DAS ON

Anchor Holding power/ anchor mass in air. As per BS-6349 Part-6-1989, the Anchor efficiency for stock anchor in poor to Good Go od soil is 5 (Average (Average of 5 & 10). Based on this the anchor holding power po wer with factor of safety was calculated and checked. 3.1.4

Placement of the bent angle and straight angle as per

drawing over the already made pedestals at yard as per drawing were done (Refer Fig. 14).

Revised Methodology Adopted for Caisson Foundations

The methodology for fabrication and erection of caisson had been revised to minimize the time of execution.

Accordingly the Caissons in Modules were prefabricated. Fabrication of K-lift (5.1 m + 1.6 m = 6.7 m) and required Modules of 2.4 m height in the fabrication yard

were executed during the monsoon period. Prefabricated Modules of Caisson were shifted at Launching Bed after cutting in segments as per pre approved cutting plan. Reassembling of Caisson Modules at Launching Bed

up to 6.7 m was done. Floating and placing the Caisson at location with the help of wire ropes & pulley as per tethering arrangement drawing were executed. Target had been kept for Caisson Floating in November’10. Addition of required pre fabricated modules and placing

Fig.14 Placement of the bent angle

Fixing and welding of 8 mm thk. outer skin plate upto 0.8 m height throughout the outer portion, Fixing the


297

For extension of 1.6 m (Module-1) Frames were fabricated in fabrication yard followed by erection and alignment of the frames over the curb of 5.1 m height.

Welding of the frames temporarily with curb frames was done. Placing the hoop angles, cross bracings as per drawing and welding the same with frames were done. Placement and alignment of the inner and outer

Fig. 16 Fixing the diaphragm angle

Placing of the vertical frames (Both A type & B type) as per drawing and aligning the same were done (Refer Fig. 17).

skin plates in position and welding temporarily with bottom plate of well curb were done. done. Other welding like skin plates with vertical frames & hoop angles are then completed. Complete welding of caisson up to K-Lift (5.1+1.6 m), except the joints where caisson will be cut for making pieces for shifting were done. Fabrication and erection of further required Modules at fabrication fabrication

yard were then executed (Refer Fig. 19).

298

DAS ON

Cutting of Caisson being done (Refer Fig. 21).

The top module i.e. Module-3, were cut after appropriate numbering and the same were stacked with the help of Crane. In the same way the Module-2 and Module-1 was cut and stacked. Subsequently, Subsequently, required nos. of Modules were fabricated, cut as per cutting plan, dismantled & stacked in the same manner before shifting to the location. Suitable cross bracings, stiffeners for strengthening,

lifting hooks were also provided in all components before dismantling dismantling.. Shifting Shifting of Prefabricated Prefabricated Caisson Caisson

Module by Trailer were done thereafter (Refer Fig. 24). Fig. 21 Cutting of Caisson in Modules

Lifting of Cut Piece (1.6 m Height) & Lowering and stacking the pieces appropriately at yard were done (Refer Fig. (Refer Fig. 22).


Erection of Caisson at Launching Bed were done. The pieces of Module-1 were placed as per pre marking at erection platform, followed by alignment and leveling the pieces perfectly. Welding of the vertical & other joints temporarily were done. Placement of the prefabricated frames of Module-2 (3.2 m) over the Module-1 were then done. Welding of the frames temporarily with Module-1 frames were executed. Placing the hoop angles, cross bracings as per drawing and welding the same with frames was done. Placement and alignment of the inner and outer skin plates in position and welding temporarily with bottom plate of Module-1 were then done. Other welding like skin plates with vertical frames & hoop angles were then completed. In the same manner Module-3 (3.2 m) were erected above Module-2 (Refer Fig. 26).

299

Grabbing from inside the dredge hole and as well as from outside the caisson were executed. Sinking the caisson as per reqd. draft for Floating/ Launching of Caisson were done. Dismantling of coffer dam to allow water to enter in the assembly area of Caisson were then executed. Grabbing continued till the caisson floated into water (Refer Fig. 28).

Fig 28 Grabbing inside the Caisson for Floating into the water of Caisson Caisson was towed to location with three nos. of high

300

DAS ON

Fig. e Fig. a

Fig. b


level. Caisson Modules were added further, concrete was placed and sinking done until the Caisson reached up to safe gripping length. In the above operation, the alignment of Caisson was checked in every half an hour by total station and control points. The nal adjustment of alignment was done with the help of winch arrangements. In all stages the free board was kept not less than 2.0 m. After Caisson reached the safe grip length (Minimum 1/3 of total depth of water), concreting was done up to the top of Caisson and all tethering arrangements were

301

Initially concrete was poured at caisson by Crane & Bucket method to prevent tilting in oated condition. 7 nos. of Tremie pipes were attached with the Hopper from the top of Caisson. During concreting necessary

care were taken to prevent Tilting Tilting of Caisson. Total fabrication and erection involved in P2 Caisson was 390 MT (40.3 m ht.) & for P3 Caisson was 225 MT (21.9 m ht). 7 days time cycle was achieved for a 2.4 m lift module including erection, t up, welding, reinforcement xing, winch lifting and concreting, whereas in earlier season it took 12 days per 2.4 m lift.

removed. After adopting this revised methodology, both the Erection of Further Modules at Location were done (Refer Fig. 31).

Caissons were successfully grounded by 30 th Dec’10. Both the Caissons (P2 Caisson ht. = 19.5 m and P3 = 14.7 m at the time of Grounding), were erected, oated and grounded only in 74 days and saved a time of 53 days in comparison to earlier season (refer Table 2). Detailed break up of Time saved due to Revision in

302

DAS ON

4

INITIATIVES TAKEN IN EDGE CONSTRUCTION

CUTTING

4.1

Cutting Edge Fabrication & Erection Methodology Adopted in 2010-2011 2010-2011

Cutting edge used to be fabricated at fabrication yard

up to 1.0 mtr height (Refer Fig. 33).

Fig. 35 Erection of Fabricated Modules of Cutting Edge

The Cutting edge modules were then shifted to location by Tusker Tusker (Refer Fig. 36).

Fig. 33 Cutting Edge Fabricated up to 1.0 mtr. height


Cutting edge Modules were erected up to 2.0 m height at location (Refer Fig. 38).

5

303

CONCLUSION

As time being the essence in construction of Bridges in river Brahmaputra, so the primary objective was to minimize the time of execution to fullest extent.

In this paper, the engineering solutions derived, after adopting the revised & innovative methodology in

executing the Caisson foundation & fabrication/ erection of cutting edge at location in mighty and

ferocious River Brahmaputra would immensely be benecial for Engineering Profession, as it involves substantial reduction of time of execution by 42% for caisson foundation & by 60% for fabrication & erection Fig. 38 Cutting edge modules erected

Erection of Cutting Edge was then completed (Ref. Fig. 39).

of cutting edge at location. The successful completion of this highly technical & ambitious project of North East Frontier Railway will not be, just a routine completion of bridge, but the execution of this bridge, especially the revised & innovative methodology adopted in executing the Caisson foundation & fabrication/ erection of cutting edge at location in mighty and ferocious River Brahmaputra, certainly exhibits the story of meticulous

Paper No. 603

LANDSLIDE HAZARD DAT DATABASE AND INVENTORY IN VENTORY-- FOCUS ON A SUITABLE METHODOLOGY FOR INDIA ISHOR K UMAR ** SHANAL PRADHAN*, K ISHOR K UMAR ** AND S. GANGOPADHYAY***

ABSTRACT The databases and inventory of the landslides are the backbone of effective landslide hazard and risk management in any part of the world. A systematic database and inventory of landslide events is valuable for many reasons, mainly locating the la ndslides spatially, connecting through historical background with the current ground realities, x-raying the conditions and causes of their recurrences and correlating with ground conditions, estimating human and economic losses for evaluating landslide predictions and their effective risk management. At the same time it is a challenging task to prepare a national landslide database for a country as huge and diverse like India. Many countries which are vulnerable to such disasters have developed their own databases. In this study a review of available databases of different countries have been carried out. A methodology for the development of landslide database for India is suggested.

1

INTRODUCTION

Worldwide there are numerous landslide databases all of them with a common objective to study the evolution of landscapes, and are mandatory to ascertain

landslide susceptibility, susceptibility, hazard and risk (Komac, M., et

exposed (180,254) i.e.; the number of people present in hazard zones that are subject to potential losses and 9th out of 162 on GDP exposed 1.07 (billion US$) i.e.

NVENTORY-FOCUS LANDSLIDE HAZARD DATABASE AND I NVENTOR

amount of GDP (Gross Domestic Product) present in hazard zones that are subject to potential losses (preventionweb.net in Kumar et al., 2011; 2009 Global Assessment Report). Of all the world’s landslides, 30 per cent occur in the Himalaya, according to a South Asian Association for Regional Cooperation

(SAARC) study on the causes and consequences of natural disasters in the region. The natural ecosystem

ON A SUITABLE METHODOLOGY FOR I I NDIA

305

their business/trade, inability to provide medical aids to the critical patients and also creates social unrest amongst the communities living at both the sides of the blockade location because of their inability to attend the social obligations, hardship in reaching the destinations through the tougher and longer alternate routes. Every time the tragedy strikes, huge amount of budgetary funds are pumped into the rehabilitation and

of the mountainous terrains of Himalaya is often characterized by unfavorable geological, topographical and seismic conditions making it highly susceptible

restoration works without giving least thought to pre-

for geo-environmental hazards. States of Jammu and

process repeats again and again. The restoration and

Kashmir, Himachal Pradesh, Uttarakhand, Arunachal

Pradesh, Nagaland and Manipur comes under high to very high hazard zones. Northeastern regions like Darjeeling district of West Bengal, Sikkim, Tripura,

rehabilitation process never gets completed. Direct losses such as the costs of repair and maintenance, restoration, rehabilitation or the replacement of the damaged properties is met out of maintenance budget

Meghalaya, Assam, Mizoram, are badly affected by landslide causing chronic problems and all kinds of losses. Hilly regions of Karnataka, Andhra Pradesh,

allocated for the whole year; as a result, overall maintenance of the roads is also affected (Kumar et al., 2001). Fig. 2 depicts some of the landslides that have

Tamil Nadu, Maharashtra, Goa and Kerala constitute low to moderate hazard zones. Fig. 1 shows zone wise

disaster planning. By the time these affected areas are rehabilitated, monsoon reappears again and this vicious

occurred in different states.

306

PRADHAN, K UMAR UMAR & & GANGOPADHYAY ON

most probable causative factors for their occurrences

(Hilker, N., et al.2009). According to Kumar and Jangpangi., 2009, landslide database and inventory map of existing landslides is an important and, in fact, rst step towards landslide hazard assessment, management and mitigation studies. It not only provides information about current situation of landslide areas but also provides opportunity to validate and correct the landslide susceptibility potential maps, if already prepared.

This can also be used for knowing recurrent and old but quiescent landslides (Gangopadhyay and Kumar, 2009). With the presence of database we can compare with other foreign databases on a regional or national level, which is valuable in order to improve our own methods and techniques. Evaluation of vulnerability vulnerability and risk requires a sound base of documents and

records including past and present disasters. It gives an estimation of the degree to which landslide occurrence is increasing with time. Landslide database facilitates old data and the introduction of new data and manages

1996; Castellanos Abella et al., 1988; Carrara et al., 2003). In Europe, USA and Mexico, different groups and organizations have developed landslide databases.

The records include information of geotechnical, lithological and geomorphological data from individual

landslide sites. International activities for establishing a Worldwide Landslide Database are in progress under the auspices of ‘The International Geotechnical Societies Societie s ‘UNESCO Working Party on World World Landslide Landslid e Inventory’ in cooperation with the International Association of Engineering Geology (WP/WLI 1990; 1991; 1993). In France the national landslide (BDMvt) has been in operation since 1994 and is maintained

by the French Geological Geological Survey (BRGM) with the nancial sup port sup port of governmental governmental institutions institutions (BRGM, 2007). The Swiss Federal Research Institute WSL has been collecting information on ood and landslide damage in Switzerland since 1972 (Hegg&Fraefel, 2005). There are several national databases comparable to the Swiss one (Australia: Blong, 2004; Ireland: Creighton, 2006; Italy: Guzzetti and Tonelli, 2004;


concerning landslide problems in this country. Devoli

et al., (2006) has used all other sources (e.g. newspaper,


307

understanding and mapping of these hazards will be built to better cope with future landslide hazards in a

old chronicles, and historical monographs at public archives, technical reports and natural disaster database,

form of mitigation and managing.

international journals) other than eld evidences to prepare national landslide database of Nicaragua

4

analyzing both temporal and spatial distribution, types of landslides, triggering mechanisms, and type

Within our country a few studies have been attempted to provide information to meet identied management objectives, there has been less effort spent on the provision of a systematic information base. In India

of damage of the recorded historical landslides. The AVI inventory (Italian acronym for Italian Affected Sites [by mass movement and oods]) constitutes the most extensive records available at national scale,

which only few other countries have accomplished. Hong Kong landslide inventory has used statistical correlations of landslide frequency and terrain variables

to allow the production of landslide susceptibility susceptibility maps (Dai and Lee 2002). The Australian landslide landslide database, managed by Geoscience Australia, brings together three separate inventories and has concentrated on improved

interoperability (Osuchowski and Atkinson., 2008). The on-line database and map represents the spatial

CURRENT LANDSLIDE RESEARCH IN INDIA

there is no centrally organised landslide database, although some initiatives have been taken at the local level that cover localized areas.

However, lack of standardization and varying scales of information within the existing databases make it difcult to perform empirically-based statistical hazard analysis and to identify controls on magnitude and

frequency as well as to establish regional comparisons of landslide activity (Glade. T, Crozier. M. J., 1996). The inconsistent record also makes it difcult to interpret

308


and laboratory analysis were undertaken by them in the pre-eighties and are now focused on scientic

there are compelling social, economic and legislative reasons for obtaining and assessing information on

investigation, instrumentation, monitoring and controlling of landslides through large scale mapping,

landslide activity. activity. As a way of improving our currently weak information base, recommendations are given for

hazard zonation, remote sensing and GIS and other new

establishing a database information system appropriate

technologies for effective management of landslides. A

for Indian conditions.

database of around 250 landslides has been prepared by CRRI (Gangopadhyay and Kumar, 2009). CRRI

5.

has attempted to create an engineering database on landslides based on Relational Database Management

technique. It includes information on a variety of data related to geography, geology, geotechnical characteristics of different landslides. Central Building

Research Institute (CBRI) has also made an inventory of landslides on Rishikesh-Badrinath and RishikeshKedarnath routes in the Garhwal Himalaya. In recent years, landslide inventories have been

PROPOSED METHODOLOGY OF THE DATABASE

The proposed methodology suggested is based on the processing of large amount of literature from

international as well as national experience on databases and inventory. inventory. It is structured in the following way: 1. Data collection methodology 2. Database structure

prepared and updated by utilizing data from aerial photographs and high spatial resolution resolution remote sensing

3.

Web-based user interface

images obtained from satellites such as IKONOS

4.

Dissemination of data: Web-GIS



309

The usual methodology followed by most countries is the government government body body which is the main authority for

wherein the main central agency will co-ordinate and

this purpose. But many problems and challenges arise

be adopted in India. The regional bodies can consist

with a huge and diverse country like India. Extraction

of states or areas demarcated accordingly to their

and maintenance of information by a sole agency is

likelihood of susceptibility. Based on these views, a data collection strategy is suggested below.

impractical and impossible. Problems of non-uniformity arise when a large number of individuals are involved. The central government takes the main responsibility in countries like Australia, Nicaragua, Norway, Norway, Slovenia, Italy, and Switzerland. Therefore, keeping in view the conditions suitable for Indian scenario, a simple yet ingenious method used by Italy for their AVI Project,

direct the activities of a number of regional bodies can

The working plan for collection of data consist of a Central Coordination Unit (CCU) or a national institution, whose task will be to organize, oversee and direct the activities of different Regional Teams (RT) (Fig 3).

SOURCE OF DATA

R&D

Earth,

User

Institutions

Science

Agencies

Department, Ministries

NGOs

Public

Interview of

Libraries

Locals, Scientists, E x ert s

Internet

310


within their jurisdiction, with the help of survey forms given below (Fig 4). Data forms are utilized for the entry and retrieval of attribute data. The form presente pres entedd here h ere is a simple simpl e one, o ne, with limited limit ed number numbe r of possible entries to better adapt to our conditions though an extensive Porforma has been provided in

Special Report-15; IRC; 1995; Towards a national landslide information base for New Zealand Database (Glade T., Crozier M. J; 1996). Geological Survey

of India has provided a brief information sheet for landslide incidences (www.portal.gsi.gov.i n). Along with the form, the Research Teams will collect the available information in the form of literature, aerial photos, and maps of the concerned landslides

as shown in Fig. 3 from various sources (Fig. 3). This form along with the gathered information is then digitized and used for counting the number of landslides taken place. British Geological Survey has

LANDSLIDE INFORMATION FORM

Landslide ID

Survey No

Name of Surveyor Surveyor

GENERAL INFORMATION

Name of Slide Location :

Type of Slide Toposheet No

On /Off Highway

Coordinates

Village / Town

Causative Factor

Tehsil / Taluka

Site Description

Lat

Long


•

Review the list of data to be collected.

•

Synthesize and verify the information collected


by the RT and assembling it in an electronic format.

•

Facilitate the making of decisions with regard to appropriate map scale, datum, ellipsoid and

projection. •

Should be the national counterpart to facilitate

transfer of knowledge, (disseminating information), public awareness, emergency response, maintenance and updating of the information. 5.2

Database Structure

The general includes: 1.

structure of database as shown in Fig. 5

The digitization of landslide spatial locations using

Fig. 5 Structure of Database

311

312


and managed via a GIS. The link between spatial data themes and attribute data is done on a one-to-many basis, where the whole dataset is linked by a similar ID allotted to them (Fig. 6).

5.3

Web Based User Interface

Database collection is a continuous process, therefore updating facility must be provided not only to

administrators but also to users, allowing different users to use the internet ap plication ap plication for registering and

reporting new landslide events, and making additional changes or correcting the data already stored. In order to secure the database, all users have to register and

Fig. 6 Entity relationship diagram of datasets

After the linkage is attained, data is stored in RDBMSOracle and linked to a GIS. Integration of GIS and RDBMS into web-based client service environment will allow efcient management of wide variety of landslide data (Fig. 7). RDBMS is a program module

access the database via a user name and password. In this way the administrator can identify the person reporting the slide. This updating facility page will be provided in the WebGIS platform under the updating option. The update given will not be directly input into the databank (RDBMS), but rst veried by the database administrators. This allows the administrator to identify the person who reports a slide. New entries will be continuously evaluated by the database administrator.


standard Internet browser (e.g., Mozilla Firefox©, Microsoft Internet Explorer©, Opera©) and without specic or proprietary software on the computer client (e.g. Applets Java, Active Active X) (Salvati (S alvati et al., 2009). This system combines the potential of both Internet and GIS technologies; the GIS provides the capability for


313

government authorities, disaster and road management

committees, National/State Highway authorities, land use, housing and urban planning departments,

international agencies and NGOs along with the general public working on prevention and mitigation of risks posed by landslides. landslides.

storing and managing large amounts of spatial data,

while Internet technology allows easy access to the geospatial information (Nasaruddin et al., 2011). This dynamic virtual visualization process through a web platform brings an insight into the understanding of the landslides and the resulting damage closer to the

affected people and user community (Das et al., 2012). Disseminating spatial information on the internet

improves the decision making process. For example a specic web site (http://eventistoriciumbria.irpi.cnr. it) was designed to disseminate the available historical information, and WebGIS technology was adopted to show the location of the sites affected by historical landslides in Umbria, Italy. Iranian System for Road Information has also adopted WebGIS technique in

ACKNOWLEDGEMENT

Authors are thankful to Shri Anil Kathait, Mrs. Lalita

Jangpangi and Sh. Indervir Singh Negi, CRRI for their suggestion and help during the preparation of this paper. paper. REFERENCES

1.

Komac, M., Fajfar, D., Ravnik, D., Ribicic, M; Slovenian National Landslide Database –A promising approach to slope mass movement

prevention plan; GEOLOGIJA; doi:10.5474; 393–402.

50/2;

314

7.

8.

PRADHAN, K UMAR UMAR & & GANGOPADHYAY ON LANDSLIDE HAZARD DATABASE A ND I NVENTORY NVENTORY- FOCUS O N A SUITABLE METHODOLOGY FOR I I NDIA

Hilker, N., Badoux, A., Hegg, C; The Swiss ood and landslide damage database 19722007; Natural Hazard Earth Syst. Sci; 9; 2009; pp. 913-925

15.

oriented image analysis. 16.

Jaedicke, C., Lied, K., Kronholm, K: Integrated database for rapid mass movements in Norway; Natural Hazards Earth Syst. Sci; 9; 2009; pp. 469-479.

Uttarakhand Himalaya

17.

Gangopadhyay. S., Kumar. K; Safety and efcient management of road network in landslide prone areas; Science and Culture, Vol.75, No 11-12; Nov.-Dec. 2009.

Dikau, R., Cavallin, A., Jager, S; Databases and GIS for landslide research in Europe; Geomorphology 15:227-239; 1996.

18.

Das, I., Oberoi. K., Roy, P.S; Database Organization in a web enabled free and open source software(FOSS)environment for Spatiotemporal analysis modeling; ISPRS Annals of the Photogrammetry; Remote Sensing and Spatial Information Sciences; Volume I-4; 2012.

19.

Salvati, Paolo., Balducci, Vinicio., Bainchi, C., Guzzetti, F., Tonelli, G : A WebGIS for

Kumar, K., Jangpangi, L., Mathur, S; Prominence and state of the landslide hazard

inventory and zonation along highways in 9.

Martha, T.R; Detection of landslides by object

10.

Management of landslides and avalanches., NDMA, June 2009.

snow

11.

WP/WLI (International Geotechnical Societies=UNESCO Working Party on World Landslide Landslide Inventory), 1991: A suggested method for a landslide summary–Bulletin International

Paper No. 604

EVALUATION OF DESIGN OF GEOCELL REINFORCED UNPAVED ROADS JYOTHI P. P. MENON*AND G.L. SIVAKUMAR BABU**

SYNOPSIS In India more than 40% of the roads are unpaved which are mostly made without any surfacing of asphalt concrete layers and classified as rural roads. As these roads play very important role in overall economic development of a country, design of these roads require priority. In order to prevent the failure of unpaved roads due to poor subgrade CBR, geocell reinforcement can be used in a n effective manner. In the present work the design method developed by Pokharel (2010) for geocell-reinforced unpaved roads is examined for evaluating the e ffectiveness of geocells as reinforcement for granular base courses over weak subgrade. The effectiveness is evaluated in terms of required base course thickness for poor subgrade CBR values. The effect of various factors like subgrade CBR, base CBR, allowable rut depth and number of passes of axles on the required base course thickness are analyzed in a detail manner.

1

INTRODUCTION

Rural roads and access roads to various resource industries lead to economic development in all

countries. Construction of unpaved road section with poor subgrade CBR values is very difcult and leads to insufcient structural stability. According to the

behavior of geocell geocell reinforced soil during the last three

decades. These works were based on experiments and numerical simulations; for example Rea and Mitchell (1978), Mitchell et al. (1979), Bathurst and Jarrett (1989), Bush et al. (1990), Bathurst and Karpurapu (1993), Cowland and Wong (1993), Rajagopal et al. (1999), Madhavi Latha et al.(2006), Madhavi Latha

MENON & BABU ON

316 2

OBJECTIVE OF THE STUDY

The major objective of this study is to evaluate the effectiveness of geocells in inducing connement effect for granular base courses over weak subgrade. The effectiveness is evaluated in terms of required base course thickness for poor subgrade CBR CB R values.

The design method developed by Pokharel (2010) for geocell-reinforced unpaved roads is used for the study. 3

geocell-reinforced unpaved roads. The studies done by Pokharel (2010) show that geocell reinforcement signicantly slowed down the rate of deterioration in the base quality. This phenomenon is attributed to the geocell connement of the base course to increase and maintain the modulus of the base course. A modulus

improvement factor was proposed by Han et al. (2007) to account for this benet [Eq.2]

DESIGN PROCEDURE

A brief description of the development of design method

by Pokharel (2010) method is as follows. The basic design Eq.(1) developed by Giroud and Han (2004a and b) can be used to estimate the required base course thickness (h) of unreinforced and planar geosynthetic (geotextile and geogrid) reinforced roads:

...2

where E bc (reinforced)= the modulus of the reinforced base and E bc (unreinforced)= the modulus of the unreinforced base.

For unreinforced and planar geosynthetic-reinforced roads, Giroud and Han (2004b) recommended the maximum limit of the modulus ratio (R E) as 5 considering that base courses cannot be well compacted over soft subgrade. However, the three-dimensional connement

EVALUATION

OF DESIGN OF GEOCELL R EINFORCED EINFORCED U NPA NPAVED R OADS OADS

1.

Conduct static plate loading tests for multiple geocell reinforced base material and for unreinforced conditions.

2.

The modulus improvement factor ‘I f ’ can be

...4

Since a nonwoven geotextile sheet is commonly used below geosynthetic-reinforced geosynthetic-reinforced bases, the bearing capacity factor (Nc) for geocell-reinforced unpaved

obtained as the ratio of the slope of the linear

portion on the pressure-displacement curve of the reinforced section to that of the unreinforced section.

roads can be reasonably assumed to be equal to 5.14

(Giroud and Han, 2004a). Giroud and Han (2004b) proposed a factor (‘k’) that controls the rate of reduction in the stress distribution angle which depends on the (r/h) ratio and the aperture stability modulus of geogrid. Obviously, the aperture stability modulus is not suitable for geocells, a factor (‘k’) is proposed by Pokharel (2010) to replace the term (0.661-1.006J 2) (r/h)1.5 in Eq.1. The resulting equation for the design of geocell-reinforced bases over weak subgrade is as follows:

...5

317

3.

Determine CBR bc and CBRsg

4.

Knowing ‘If ’, CBR bc and CBRsg, calculate ‘R E’ using Eq.3.

5.

Carry out static plate loading tests and moving

wheel tests for different base and geocell thicknesses. 6.

The number of loading cycles (or passes in case of moving wheel tests) ‘N’ can be directly obtained from the tests. The applied pressure ‘P’ and the radius of tire contact area (r) should

318

MENON & BABU ON

For the present analysis Eq. (7) has been considered for determination of k’ and the following formula is used to estimate the thickness of the geocell-reinforced

5%. The required base thickness is determined for three subgrade CBR values 1, 3 and 4%. The subgrade soil was assumed to be saturated with low permeability like

base:

silt and clay. Consequently, its shear strength is same as its undrained cohesion, c u. The value of undrained shear

...8

4.

DESIGN PARAMETERS

4.1

Geometry of Pavement

A uniform thick layer of subgrade reinforced with one layer of NPA geocell at the interface between base course and subgrade soil is assumed in the analysis.

The base thickness of the reinforced sections included 2 cm top ll cover with the same material as the inll one. The Fig.1 gives typical section considered for the analysis. A minimum minimum thickness of 0.1 m is adopted for base course to reduce the disturbance of subgrade soil

during trafcking and to provide sufcient anchorage

strength (cu) was approximately deduced from the CBR value of the subgrade soil (for CBRsg less than 5) using the Eq. 6. A uniform thick base course with 10 and 20% CBR values was assumed in the present analysis. The modulus improvement factor (I f ) was assumed to be 1.7 in the present study. The modulus of the unreinforced material was multiplied by ‘I f ’ for the thickness equal to the height of geocell plus 2 cm

cover. The remaining thickness of the base course was considered as unreinforced and no modulus improvement factor was applied. The nal modulus was then calculated by taking the weighted average of the two values. 4.3

Trafc and Standard Axle Loads

EVALUATION


319

1993) recommend allowable rut depths from 13 to 75 mm for low volume road design. Considering the AASTHO guidelines two allowable rut depths of 60, 75 mm were considered in the analysis. 5

RESULTS AND DISCUSSIONS DISCUSSI ONS

The base course thickness of the unpaved section for unreinforced and geocell reinforced sections were determined for subgrade CBR values of 1, 3 and 4%. Separate curves were obtained for different N values (N= 100, 1000, 10000, 100000). The results include plots for allowable rut depths of 60 and 75 mm as well as for CBR base = 10 and 20 per cent. The effect of CBR sg, CBR base, allowable rut depth and number of passes of axles on required base course thickness are

described in the following sections. 5.1

Effect of Subgrade CBR values

The required base course thicknesses for unreinforced and geocell reinforced roads were determined

Fig. 3 Required base course thickness for allowable rut depth of 75 mm (CBR base=20%)

320

MENON & BABU ON

10% the base thickness is 58 cm for unreinforced and 28 cm for reinforced case. The same is 51 cm and 24 cm for CBR base 20% (Fig. 3). From Fig 4, for N=100000, CBR sg= 1%, allowable rut depth of 60 mm and CBR base 10% the base thickness is 65 cm for unreinforced and 33 cm for reinforced case. The same is 57 cm and 28 cm for CBR base 20% (Fig. 5). The Tables 2 and 3 show the percentage reduction in the base course thickness between unreinforced and reinforced section for 10 and 20% of CBR base values

Table 3 Base Course Thickness Reduction Percentage For CBR base= 20% Allowable rut depth 75 mm

100 103

respectively. 5.3

N

CBR sg

Effect of Allowable Rut Depth on Thickness of Base Course

Allowable rut depth 60 mm

N

CBR sg

104 10 5

100

103

10 4 10 5

1

57.57 55.64 53.23 51.39

1

55.21 52.5 52.54 4 50.61 58.39 55.21

3

66.86 66.86 64.6 64.677 60.0 60.011 55.8 55.888

3

64.51 59.21

4

73.16 73.16 74.1 74.122 71.9 71.922 65.8 65.822

4

70.10 65.11 59.01 54.30

54.57 51.19

Referring Table 2 and 3, percentage reduction in the base course thicknesses is more for 75 mm m m allowable rut depth case. Same trend is identied for both CBR base 10 and 20% cases.

6

5.4

in unpaved roads. All the results points to one main conclusion that there are considerable savings in the

Effect of Number of Passes of Axles (N)

CONCLUSIONS

This paper presents the utility of geocell reinforcement

EVALUATION

2.

3.

4.


Bathurst, R.J. and Jarrett, P.M. (1988). “Large-

Scale Model Tests of Geocomposite Mattresses Over Peat Subgrades.” Transportation Transportation Research Record 1188, pp. 28-36. Bathurst, R.J. and Karpurapu, R. (1993). “Large-scale Triaxial Compression Testing of Geocell-Reinforced Granular Soils.” Geotechnical Testing Journal, GTJODJ, 16 (32), pp. 296-303. Cowland, J.W. and Wong S.C.K. (1993). “Performance of Road Embankment on Soft Clay Supported on a Geocell Mattress

5.

Foundation.” Geotextiles and Geomembranes, 12 (8), pp. 687-705. Giroud, J.P. and Han, J. (2004a). “Design Method for Geogrid-Reinforced Unpaved Roads. I. Development of Design Method.”

11.

6.

Pok harel,

S.K. (2010). Experimental Study on Geocell-Reinforced Bases Under Static and Dynamic Loadings. Ph.D. Dissertation, CEAE Department, the University of Kansas.

12.

Rajagopal, K., Krishnaswamy, N.R., and Madhavi Latha, G. (1999). “Behaviour of Sand Conned with Single and Multiple Geocells” Geotextiles and Geomembranes, 17 (3), pp. 171-184.

13.

Rea, M. and Mitchell, J.K. (1978). “Sand Reinforcement Using Paper Grid Cells.”

Regular. Meeting- Rocky Mountain Coal Mining Institute, 644-663. 14.

Sivakumar Babu, G.L. and Pawan Kumar. (2012). “An Approach for Evaluation of Use of Geocells in Flexible Pavements.” Journal of Indian Roads Congress, Paper No. 578, pp. 159-168.

15.

Steward, J., Williamson, R., and Mohney, J. (1977), “Guidelines for Use of Fabrics in

Journal of Geotechnical and Geoenvironmental

Engineering, 130 (8), pp. 775-786. Giroud, J.P. and Han, J. (2004b). “Design Method for Geogrid-Reinforced Unpaved

321

Paper No. 605

ANALYTICAL ANALYTICAL DESIGN OF SHORT PANELLED PANELLED CONCRETE PAVEMENTS M.V. ARUN CHAND* AND B.B. PANDEY** ABSTRACT Concrete pavements are not very common in India due t o its higher cost though the well-constructed ones last much longer without any maintenance. The paper presents an analytical solution for stresses in short panelled concrete pavements so that thin concrete slabs can be used for village roads, highway highways, s, bus and truck parking areas and toll plaza. Finite Element method is used for the computation of maximum exural stresses for slab of different sizes. Flexural stresses caused by wheel loads of any magnitude can be accurately computed. It is found that the stresses are drastically reduced by reducing the slab size. Examples are solved to illustrate design of thin concrete pavements for (i) a village road and (ii) for a toll plaza.

1

1.1

INTRODUCTION

cemented treated granular layer, stabilised soil or dry

Bituminous pavements are commonly favoured

lean concrete depending upon the trafc and drainage conditions. For each of the above panel sizes, stresses were computed without load transfer across the joints

for most roads in India because of the high initial cost of concrete pavements. Bituminous pavements of majority of city streets as well those of state and district district roads get damaged within two years of their construction

so that a designer can select appropriate pavement thickness for pavement design. Load transfer at the

joints and bond with the foundation foundation add to the safety of

A NALYTICAL YTICAL DESIGN OF SHORT PANELLED CONCRETE PAVEMENTS

good bond is created between the concrete slab and the milled existing bituminous pavement. Most literatures

deal with such cases. Rasmusen and Rozycki(2) has given details of white topping and ultra-thin white topping in USA. Wen et al(3) presented details of such pavements laid over bituminous pavements in

Wisconsin state in USA. A good bond between the concrete overlay and the existing bituminous base was recommended. IRC:SP:76-2008(1) provides tentative guidelines for design of white and ultra-thin white topping. Stress computation is done using the software IITRIGID used in IRC:58-2002(4) in which empirical corrections for small size of concrete slabs are made to get the stresses for the small bonded slab for the examination of the safety of the structure.

323

full depth after repeated application of wheel loads and expansion and contraction with climate. Bond with cemented subbase cannot be relied upon in the presence of water w ater since the concrete c oncrete slabs slab s are not cast when the cementitious subbase is fresh and a good bond may not be ensured. Each panel is divided into

nite elements and springs are applied at each node to represent reaction provided by the foundation.

The nite element idealisation is shown in Fig. 2. Appropriate values of spring constant are assigned to represent the modulus of subgrade reactions of the foundation.

CHAND AND PANDEY ON

324

The dual wheel set is placed over a panel as shown in Fig. 5. The c/c spacing of the dual wheels is 310 mm. A tyre pressure of 0.80 MPa was considered in stress analysis.

of time. The friction at the interface boundary of the slab and the supporting foundation

may be reduced

to a low value due to expansion and contraction of slabs as well as due to presence of water. Hence stress computation for the case (i) only is presented in the paper. paper. Effect of load load transfer and bond bond with foundation foundation are also discussed.

The exural stresses for different different panel sizes as well as slab thicknesses are presented in Figs. 6 to 9.

Fig. 5 Wheel contact area at the edge of a concrete panel 5

STRESS COMPUTATION COMPUTATION

The commercial structural analysis package ANSYS (version-12) has been used in the present study. study. Three dimensional nite element models representing concrete slab and spring foundation system have been modelled

using the 3-D eight noded brick element SOLID45 and

Fig. 6 Flexural stress vs panel size for 50 mm thickness


325

Fig. 12 Flexural stress vs thickness of slab of size 1.0 x 1.0 m

Fig. 9 Flexural stress vs panel size for 150 mm thickness

Figs. 6 to 9 indicate that the exural stresses can be reduced drastically with reduction in slab sizes, the reduction being more than 60% for decreasing the length of panel size from 1.25 m to 0.50 m. Even a 75 mm concrete slab with panel size of 0.50 m x 0.50 m will develop a exural stress of only 2.6 MPa under a dual wheel load of 50 kN and can be a cost effective solution for village roads. A thickness of

about 150 mm is sufcient for bus bays, truck parking

Fig. 13 Flexural stress vs thickness of slab of size 1.25 m x 1.25 m

CHAND AND PANDEY ON

326

designed accordingly taking the advantage of load sharing behaviour through aggregate interlocks across

the joints. 7

EFFECT OF BOND WITH SUBBASE

If a slab gets bonded partially or fully to cement or bitumen bound subbases, stresses in the the slab is reduced.

Analysis(11) was done using CONTA 173 and Target 170 elements of the ANSYS nite element software for a 0.5 m x 0.5 m panel 100 mm thick and it is found that the exural stresses for the fully bonded case for a dual wheel load load of 60 kN is about 1.43 MPa, while

of plastic strips before placement of concrete and the

nished surfaces of a concrete slab. Wooden forms were used during the casting. It was found that the load transfer efciency dened as the ratio of deection of the unloaded edge to the loaded edge was over 90% for a well-constructed joint. Two Benkelman beams were used for the evaluation of the deections on the loaded and unloaded sides. 9

SUBBASE SUBBAS E FOR LIGHT AND HEAVY HEAVY TRAFFIC

subbase and the concrete slab is to be established over the entire life of pavements, special types of concrete

Most village roads as well as minor roads of city streets have low volume of trafc and a subbase made up of 100 mm of granular layer with marginal aggregates and 75 mm of Water Bound Macadam (WBM) are expected to perform well without loss of support. 150 mm of marginal aggregates stabilised with cement to have a seven day unconned compressive strength of

pavers can be used which can lay both the cement

3 MPa can be used instead of unbound granular layer and

concrete pavement slab and the lean concrete subbase

WBM to bring about economy. Concrete roads display

for the partially bonded case considering a friction

of 0.6 between the slab and the subbase, the stress is found to be 2.56 MPa. Bonding thus reduces the stress

considerably. If complete bond between the cemented


subgrade reaction may be taken as k=80 MPa/m (4). It may be noted that minor variation in k value has little effect upon the stresses for practical range of thickness

327

For 100 mm thick slab of panel size 1.0 m x 1.0 m subjected to a dual wheel load of 50 kN, the exural stress= 3.5 MPa (Fig. 12). If 200 kN axle load (100 kN dual wheel load) is expected, a panel size of 0.50 x 0.50 m for 100 mm thick slab gives a stress of about 3.0 MPa (double that of 50 kN wheel load).

thickness of 150 150 mm over 150 mm DLC will develop develop a exural stress of 1.70 MPa for a dual wheel load of 50 kN (Figs. 4.3 and 4.7). If the wheel load is doubled to 100 kN (Single axle load 20.4 tons), the stress is 3.40 MPa, which much less than 4.90 MPa the 90 day strength exural strength. Fatigue damage principle(4) can be used to check the safety of structure due to spectrum of axle load. For a slab of dimension 3.5 m x 4.5 m, the exural stress for 100 kN dual wheel load (20.4 Ton single axle load), stress = 4.91>4.90, hence unsafe.

Curling stresses due to temperature gradients are negligible and they need not be considered. Stress due

CONCLUSIONS

of slab. Consider M30 concrete. 90 day exural strength =4.3 MPa (Approximately).

to Westergaard equation in 100 mm thick x 3.5 m x 4.5 m slab = 6.9 4 MPa, hence highly unsafe.

A panel size of 1 .00 m x 1.00 m with with a

The following conclusions are drawn from the present study.

i)

It is seen that shorter the joint spacing, lower are the tensile stresses at the edge.

ii)

Pavements of village roads, bus bays, bus and truck parking terminals and toll plaza can be

CHAND AND PANDEY ON A NALYTICAL NALYTICAL DESIGN OF SHORT PANELLED CONCRETE PAVEMENTS

328 3.

Wen, Haifang., Li, Xiaojun. and Martono, Wilfung. (2010). “Performance Assessment of Wisconsin’s Whitetopping Whitetoppi ng and Ultra-thin White topping Projects.” WHRP, Transportation

6.

Swati Roy Maitra, Reddy, Reddy, K.S. and Ramachandra, L.S. (2010). “Load Transfer Characteristics of Aggregate Interlocking in Concrete Pavement”, ASCE Journal of

Transportation Transportation Engineering, pp. 190-195.

Research Board.

4.

IRC:58-2002, “Guidelines for the Design of Rigid Pavements for Highways”. Indian Roads Congress, New Delhi, 2002.

7.

B.B. Pandey ‘Warping ‘Warping Streses in Concrete Pavements- A Re-examination’ HRB No. 73, 2005, Indian Roads Congress, pp. 49-58.

5.

Jundhare, D.R. et al., (March 2011). “Edge Stresses and Deections of Unbonded Conventional Whitetopping Overlay”, The Indian Concrete Journal, pp. 35-44.

8.

Arun Chand, M.V. M.V. (2011), ‘Stresses ‘Stress es in Jointed Concrete Pavements’, M. Tech. Thesis, IIT Kharagpur, May 2011.

The views expressed in the paper are personal views of the Authors. For any query, the author may be contacted at: E-mail: [email protected] [email protected]

Paper No. 606

DETAILING DETAILING PROVISIONS OF IRC:112-2011 COMPARED COMPARED WITH PREVIOUS CODES (i.e. IRC:21 & IRC:18) Part 1 : General Detailing Requirements (Section 15 of IRC:112) ALOK B BHOWMICK * SYNOPSIS The new unied concrete code (IRC:112) represents a signicant difference from the previous Indian practice followed through IRC:21 & IRC:18. The code is less prescriptive and offer greater choice of design and detailing methods with scientic reasoning. This new generation code, when used with full understanding, will bring benets to all sectors of our society as it will eventually lead to safer construction and make a tangible contribution towards a sustainable society. The present situation in the industry is that most of the consulting ofces are struggling to understand this code, which is not so user-friendly. Since the designer is hard pressed for time, majority of the Consultants are unfortunately spending their valuable time only in fullling the prescribed rules of the code, acting as a technical technical lawyer, with very little understanding of the subject. In order to make use of the code effectively and to minimize the potential for any error due to non familiarity with the code, there will be the urgent need by the professional institutions, Indian Roads Congress, Ministry of Road Transport & Highways and other government authorities for organizing workshops, seminars for dissemination of the knowledge. One of the useful methods of understanding the new code in the short term is by comparing the provisions of this code with the previous practice that used to be followed prior to publication of this code. This paper is written with this objective in mind and it covers the comparative study of general detailing requirements of the present and past code (i.e. detailing provision of IRC:112 compared with detailing provisions given in IRC:21/IRC:18/IRC:78). In order to contain the length of the paper, only Section 15 of the new code pertaining to General Deta iling Requirements are covered in this paper. As a sequel to this paper, similar comparative study for Section 16 & Section 17 will also be covered in a separate paper.

1

INTRODUCTION

The new code covers detailing in much greater detail

330

BHOWMICK ON HOWMICK ON

For the benet of readers, relevant clause numbers of IRC:112 is mentioned in bracket in all heads and sub-

a) avoiding damage to the concrete when a hook or bend carries stress & causes compressive stresses in concrete inside the

heads of this paper. 2

GENERAL DETAILING REQUIREMENTS REQUIREMEN TS (SECTION 15)

2.1

Cover to Reinforcement (14.3.2, 15.3.1)

Cover to reinforcement is normally required to ensure:

a) Safe transmission of bond forces. b) Protection of steel against corrosion. c) Adequate re resistance (This aspect is not covered in IRC:112) The comparison of minimum cover to reinforcement and prestressing steel between IRC:21 / IRC:18 & IRC:112 is given in Table 1. 2.2

Spacing of Bars (15.2.1)

bend (Table (Table 15.1 of the code) and a) avoiding bending cracks in the reinforcement as a result of bending of the bars (Table 15.2 of the code). Minimum prescribed bend diameter specified in IRC:21 was dependent on bar diameter and the grade of reinforcement only. As per IRC:112, the minimum bend diameter is also dependent upon the concrete cover provided in the direction perpendicular to the plane of curvature. Larger bend diameter is mandated for bars of diameter 20 mm and above. The comparison of minimum bend diameter between IRC:21 & IRC:112 is shown in Table 2. Table 1 Minimum Cover to Reinforcement S. No.

Item

IRC:21-2000 /

IRC:112-2011

DETAILING PROVISIONS OF IRC IRC:112-2011 :112-2011 C OMPARED WITH PREVIOUS CODES (i.e. (i.e. I IRC RC:21 :21 & IRC:18)

“Severe” condition of exposure as per IRC:21 is split to “Very Severe” & “Extreme” condition of exposure as per IRC:112. 2.4

Basic Anchorage Length of Reinforcement (15.2.3)

The basic anchorage length of bars depends upon the ultimate bond strength between concrete and the rebar. The bond strength for high-bond bars are a function of type and condition of reinforcing bar, tensile strength

of concrete (f ctk,0.05), concrete cover, bar spacing & transverse reinforcement. Depending upon the location

of bar, the bond condition is treated as either ‘favourable’ or ‘unfavorable’. Any reinforcement above concrete layer of thickness of more than 250 mm below it is considered as ‘unfavorable’ as per IRC:112. This limit was 300 mm in IRC:21.

331

For unfavorable bond condition, the anchorage length is increased by a factor 1.43 as per IRC:112. This factor was prescribed as 1.4 in IRC:21. Increase in bond strength has not been considered in IRC:112 beyond concrete grade M60, to account for increased brittleness of concrete with increased strength. This upper limit was set at grade M40 in case of IRC:21. For reinforcement of f > 32 mm, IRC:112 has further de-rated the bond strength and provided additional rules for detailing in clause 15.2.6.

Anchorage lengths as per IRC:112 works out lesser as compared to IRC:21. This percentage reduction increases with concrete grade and is constant 40% for grade of concrete M60 and above. Fig.1 shows the % reduction in a nchorage length with grade of concrete.

Table 2 Minimum Bend Diameter of Reinforcement S. No.

1

Item

Minim nimum Be Bend Di Diameter 1.

IRC:21-2000 provisions

For Bars with Bent

IRC:112-2011 Provision

Case 1 : Cover perpendicular to plane of curvature less than

332

BHOWMICK ON HOWMICK ON

Minimum anchorage length in tension as per IRC:112 is maximum of [0.3 x ld; 10φ; 100 mm] & minimum anchorage length in compression is maximum of [0.6 x ld; 10φ; 100 mm]. Minimum anchorage length as

per IRC:21 was 0.33 x ld irrespective of whether the bar

lap length as per IRC:112 is substantially less than the IRC:21. Fig. 2 gives the comparison. 2.7

Transverse Reinforcement at Laps (15.2.5.1 (3) (b))

is in compression or tension.

Anchorages of shear reinforcements or links are normally to be achieved by using bends, hooks or by

welded transverse reinforcements. Use of welded bar for stirrup is a new addition in IRC:112, which was not there in IRC:21. Also there is a change in the dimension of bends and hooks compared to IRC:21 provisions, for which reference may be made to Fig. 15.3 of the code. 2.6

Splicing of Bars (15.2.5)

Splicing or reinforcement can be done by lapping,

welding or by mechanical devices. The maximum clear space between two lapped bars as per IRC:112 should not be more than lesser of (4 φ; 50 mm). In case the clear space provided is more than above, lap length shall be increased by a length equal to the clear space.

This requirement was 40 mm in IRC:21.

Need for transverse reinforcement at lap splices is recognized in both the codes. However, IRC:21 only mentioned about the requirement of providing minimum

reinforcement without quantifying it. IRC:112 has covered this aspect in much greater detail. Transverse tension arises at the location of anchorage of bar, as

shown in Fig.3. As per IRC:112, in case the diameter of the lapped bars is less than 20 mm or in case the area of the lapped bar is less than 25% of the total total area of bars, minimum transverse reinforcement provided for other reasons are

sufcient and no additional transverse reinforcement is required. In case the above condition is not satised, the total transverse reinforcement shall be provided

between longitudinal reinforcement and the concrete


used and 0.42% when micro alloys / low alloys are not used. Also, as per IRC:21, for HYSD bars, only 80% of the area of welded bar could be taken as effective for design purpose at the location where it is welded. This condition is withdrawn in IRC:112.

333

suppliers, acceptance testing shall be carried out in

laboratories rst, before choosing the system. 2.10

Additional Rules for HYSD Bars Exceeding 32 mm in Diameter (15.2.6)

This is a new clause in IRC:112 and did not exist in IRC:21. For HYSD bars with φ > 32 mm, lapping is generally not permitted as per IRC:112. Such bars shall be either butt-welded or joined using mechanical devices. Exceptions to this can be made in situations

where minimum dimension of the member lapped is 1m or the stress in the reinforcement does not exceed

80% of the design ultimate strength. 2.11

Fig. 2 Percentage Reduction in Lap Length as per IRC:112 compared to IRC:21

Use of Bundled Bars (15.2.7)

Unlike IRC:21, the new code, IRC:112 has detailed provision for bundled HYSD bars. bars. It allows bundles bundles of upto four bars in compression zones and three bars in all other zones. All the bars in a bundle shall be of the

same characteristics (i.e. Type, Grade and preferably

334 2.12

BHOWMICK ON HOWMICK ON Prestressing Units (15.3)

IRC:112 gives minimum spacing and cover to post tensioned ducts as well as pretensioned tendons on similar lines as given in IRC:18 (for post tensioned ducts) and IRC:SP:71 for pretensioned tendons. For post tensioned bonded cables, the minimum clear

spacing between individual cables is kept as maximum of [φduct, 50 mm, dg+10 mm], where φduct denotes the outer diameter of the duct. Grouping of cables in pairs are permitted, both

horizontally as well as vertically in IRC:112 for the straight portion of the cable. This was discouraged in IRC:18. For horizontal grouping, the limiting duct diameter is 50 mm and for vertical grouping, the maximum duct diameter is limited to 110 mm. Minimum clear cover for the post tensioned ducts is given as maximum of [φ [ φduct, 75 mm]. This is a departure

from the provision of IRC:18, according to which, the clear cover is restricted to 75 mm only.

for estimation of transmission length. IRC:SP:71 gives a very simple formula, which is only dependent upon the concrete strength at transfer and the initial prestressing

force. IRC:112 formula is however quite elaborate and includes the effect of bond condition, nature of release of prestress, design tensile strength of concrete and the

tendon stress after release of prestress. The provisions of IRC:112 draws distinction between the transmission length (l pt), over which the prestressing force is fully transmitted to the concrete; the dispersion length (l disp), over which the concrete stresses gradually disperse to B-Region (region in which the assumption of plane section remaining plane is valid) and the anchorage length (l bpd), over which the tendon force at the ultimate limit state is fully transmitted to the concrete. This distinction is very aptly demonstrated in Fig. 15.11 and Fig. 15.12 of the code. For the anchorage devices used for post tensioned tendons, IRC:112 requires that the full design strength of tendons should be developed taking account of any


ducts, which will lead to increased thickness of webs and deck slab/soft slabs for PSC girders/ PSC Box girder bridges.

b)

Application of new code will lead to signicant reduction in anchorage length (10% to 40%) and lap lengths (20% to 60%) for reinforcement, as

REFERENCES

1

IRC:18-2000 : Design Criteria for Prestressed Concrete Road Bridges (Post Tensioned Concrete) (Third Revision).

2

IRC:21-2000 : Standard Specications & Code of Practice for Road Bridges SECTION: III – Cement Concrete (Plain & Reinforced) (Third Revision).

3

IRC:112-2011 Road Bridges.

compared to previous codes.

c)

For weld ability requirements of reinforcements, the Carbon Equivalent (CE) limits prescribed are diluted in IRC:112 as compared to IRC:21.

335

: Code of Practice for Concrete

The views expressed in the paper are personal views of the Authors. For any query, the author may be contacted at: E-mail: bsecmail@yahoo. [email protected] com

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