Use of Fly Ash for Road and Embankment Construction

Use of Fly Ash for Road & Embankment Construction Presentation by

Sudhir Mathur Head Geotechnical Engineering Division Central Road Research Institute, New Delhi

Major Road Construction Programmes • National Highway Development Programme (NHDP) • Pradhan Mantri Gram Sadak Yojna (PMGSY)

Necessity of alternate materials • Large quantities of construction materials required • Scarcity of good quality aggregates / soil for road construction • Waste and marginal materials like flyash • Disposal and environmental problem

Properties of Fly ash Major constituents - Oxides of silica, aluminum, iron, calcium & magnesium

Favourable properties for embankment & road construction - Pozzolanic nature -

Light weight, Non plastic High shear strength Ease of compaction Self hardening Amenable to stabilization High permeability Faster rate of consolidation

Utilization of Fly ash • Construction of embankments / backfills • Stabilization of subgrade and sub-base • Construction of semi-rigid / rigid pavements

Engineering Properties of Fly ash Parameter Specific Gravity Plasticity Maximum Dry Density (gm/cc) Optimum Moisture Content (%) Cohesion (kN/m2) Angle of Internal Friction () Coefficient of Consolidation Cv (cm2/sec) Compression index Cc Permeability (cm/sec) Partcle Size Distribution (% of materials) Clay size fraction Silt size fraction Sand size fraction Gravel size fraction Coefficient of Uniformity

Range 1.90 – 2.55 Non-Plastic 0.9 – 1.60 18-38 Negligible 300 - 400 1.75 x 10-5 - 2.01 x 10-3 0.05 – 0.4 8 x 10-6 - 7 x 10-4 1 – 10 8 – 85 7 – 90 0 – 10 3.1 – 10.7

Physical Characteristics for Flyash as Pozzolana

Physical Characteristics for Flyash as Pozzolana

Indian Roads Congress Special Publication 58 Guidelines For Use Of Flyash In Road Embankment Published in 2001

Guidelines for Use of Fly ash in Road Embankments These guidelines provide salient details regarding design and construction of road embankments using fly ash • • • • • • • • • •

Site investigations Characterization of materials Detailed design Clearing and grubbing Stripping and storing top soil Setting out Dewatering Compacting the ground supporting embankment Handling and transportation of fly ash Spreading and compaction

Fly Ash for Road Embankment Earth Cover

Earth Cover Bottom ash or Pond ash

Typical cross section of fly ash road embankment

Bituminous Top

Shoulder Granular Layer

Selected

0.5m minimum FLYASH

Earth Cover

FLYASH

FLYASH

Natural Ground Level

Typical cross section of fly ash road embankment

1-3m

Approach Embankment for Second Nizamuddin Bridge at Delhi – – – – –

Length of embankment - 1.8 km Height varies from 6 to 9 m Ash utilized - 1,50,000 cubic metre Embankment opened to traffic in 1998 Instrumentation installed in the embankment showed very good performance – Approximate savings due to usage of fly ash is about Rs.1.00 Crore

Design Consideration The following major factors weighted heavily while designing the fly ash embankment

 Adverse site condition – location of site in flood plain area  Low specific gravity of fly ash- may lose strength under submergence  Non availability of specific data and specifications of using fly ash as structural fill

Approach Embankment for Nizamuddin Bridge

Slope stability analysis of fly ash embankment (Different side cover thickness) Details

Factor of safety Case I

Case II

--

1.05

1.5 m side cover throughout

1.30

1.20

2 m side cover upto mid height and remaining portion 1 m cover

1.42

1.36

2 m side cover throughout

1.48

1.41

6 m high embankment, 1 m side cover throughout

Case I

Fly ash saturated upto mid height

Case II Fly ash saturated upto top level

Approach Embankment for Second Nizamuddin Bridge at Delhi

Spreading of pond ash

Second Nizamuddin Bridge Approach Embankment

Compaction of pond ash

Stone pitching for slope protection


Traffic plying on the embankment


Instrumentation Following instruments installed for monitoring performance of embankment – Magnetic settlement gauges for settlement – Pressure cells for base pressure – Pore pressure transducers for pore water pressure measurement

Installation of pressure cells


Installation of settlement gauge under progress


Inferences from instrumentation data – No settlement of the embankment structure (fly ash fill) – No pressure variation with in embankment body – No change in saturation level of fly ash fill

Techno-Economic Advantages • Direct saving of about Rs.One Crore in second Nizamuddin Bridge project for PWD • Additional savings to Vidyut Board, saving of precious top soil • In road projects savings to the extent of 15-20 per cent can be achieved • Savings depend on cost of transportation of fly ash

Fly ash Embankment from G.T Road to Kajouri chowk, Delhi 0.6 m x 0.8 m parapet wall Foot 1.2 path m H.F.L

.3 m (drain) ((drain)

4.0 m

Existing carriage way

7.0 m

2.0 1

Pond ash0.2 m

2.3 m

6m

1.6 m

0.5 m 1m

0.15 m, M15 concrete

Existing Embankme nt Stone pitching to be removed

1.5 m

Ground level

1.5 m

Weep holes at 12m c/c

Filter 0.2 m, thick

Stone pitching, 0.3 m thick

Intermediate soil layers (0.2 m compacted thickness)

Parameter

Pond ash

Earth cover

Sub soil

bulk

1.56 kg/cm2

2.0 kg/cm2

1.8 kg/cm2

c

0

0.15 kg/cm2

0



33o

28o

30o

Sat.condition

Factor of safety With Earthquake

Without Earthquake

At H.F.L

1.06

1.7

Sudden drawdown

1.2

1.35

Filter material by the side of toe wall

Stone pitching on filter material

Drainage system in the embankment

USE OF POND ASH FOR ROAD EMBANKMENT (Four-laning work on NH-6, Dankuni to Kolaghat, Km 17 to 72, West Bengal)

Four-laning work on NH-6, Dankuni to Kolaghat,

AGENCIES INVOLVED

• National Highways Authority of India – Client • M/s ICT, India and SNC-LALALIN,Canada –Consultant • M/s Road builders (M) Shd.Bhd, Malaysia - Contractor


TYPICAL ROAD FEATURES/CONDITIONS OF THE PROPOSED ROAD

• Length of road - 60 km • Height of embankment - 2 to 4 m • Water logged conditions • Soft sub-soil conditions


c

Existing carriage way



Typical Cross-section of Existing Highway


EXISTING CONDITION OF ROAD


EXISTING CONDITION OF ROAD OTHER SIDE


PRELIMINARY INVESTIGATION AND ASSESSMENT OF SITE CONDITIONS • Medium to High rainfall • Water table is high • Waterlogged conditions • Subsoil generally weak – Silty clay or clayey soil up to 20 m depth – SPT values in the range of 2 to 5 – C = 0.25 kg/cm2,  = 0o


NEED FOR ALTERNATIVE MATERIAL • Earth proposed in contract document.  Earth requirement –approx. 2.0 million cum.

• Haul distance more than 100 km. • High transportation cost • Delays expected in the completion of the project


LABORATORY AND FIELD INVESTIGATIONS • Characterisation of soil and fly ash • Sub-soil investigations • Stability analysis with soil and fly ash as fill materials • Evaluation of data to arrive at appropriate methodologies for construction


ARRANGEMENT FOR DEWATERING OF STAGNANT WATER


CONDITION OF THE GROUND AFTER DEWATERING


PROPOSED ALTERNATIVES FOR CONSTRUCTION

Median

Improved Subgrade of compacted thickness not less than 50 cm Granular sub-base Soil cover (1.5 m thick)

Existing embankment

Fly ash in compacted layers of 200 mm thickness

2 1

Min. 0.5 m

2m

2m

Sand or bottom ash min. 0.5 m thick

Geotextile

Temporary pond ash Proposed berm of pond ash bund after completion of embankment


SPREADING OF GEOTEXTILE OVER SOFT GROUND


SPREADING OF GEOTEXTILE OVER SOFT GROUND


SPREADING OF FLY ASH OVER GEOTEXTILE


SPREADING OF FLY ASH OVER GEOTEXTILE


COMPACTION OF FLY ASH OVER GEOTEXTILE LAID ON SOFT GROUND, (WORK ON THIS PROJECT IS IN PROGRESS)

Kalindi Road Project

SCPT Test In Progress

General Site Condition

Subsoil Investigation in Progress

Reinforced Fly ash Embankment • Fly ash - better backfill material for reinforced embankments • Polymeric reinforcing materials - Geogrids, friction ties, geotextiles • Construction sequence - similar to reinforced earth structures

Okhla Flyover Approach Embankment – First geogrid reinforced fly ash approach embankment constructed in the country – Length of embankment - 59 m – Height varied from 5.9 to 7.8 m – Ash utilised - 2,700 cubic metre – Opened to traffic in 1996 – Performance has been very good

Okhla Flyover Approach Embankment Filter M edium

Facing Panels

Pond Ash Fill

7.8 m to 5.9 m

7.8 m R einforced Foundation Mattress of B ottom ash

G eogrids

Erection of facing panels

Okhla Flyover Approach Embankment

Rolling of pond ash

Support provided to facing panels during construction

Okhla Flyover Approach Embankment

Laying of geogrids

Hanuman Setu Flyover Approach Embankment

– Geogrid reinforced fly ash approach embankment – Length of embankment - 138.4 m – Height varied from 3.42 m to 1.0 m – Opened to traffic in 1997

Reinforced Retaining Wall at Sarita Vihar Flyover

Sarita Vihar Flyover Approach Embankment – Length of embankment - 90m – Max height - 5.25 m – Embankment opened to traffic in Feb 2001 – Polymeric friction ties used for reinforcement

Laying of friction ties

Sarita Vihar Flyover Reinforced Approach Embankment

Arrangement of friction ties before laying pond ash

Compaction of pond ash using static and vibratory rollers

Sarita Vihar Flyover Reinforced Approach Embankment

Compaction using plate vibrator near the facing panels

Design of Reinforced Flyash Embankment • • • • •

Height of Wall – 8m Reinforcing Material – Geogrid Back Fill – Soil and Flyash Design of Wall- BS 8006-1995 Checks made- Internal and External Stability - F.S. against Sliding - F.S. against overturning - F.S against bearing capacity - F.S. against rupture - F.S. against pullout

No of Layers = 12

No of Layers = 16 7.4 6.8

7

6.2

6.2 Vertical Sp acing (m)

Vertical Spacing (m)

5.6 5 4.4

Soil

0

2

3.8 3.4 3 2.6 2.2 1.8 1.4 1 0.6 0.2 4

6

8

Length of geogrid (m)

5.4 4.6

0

Fly Ash

3.8 3.2 2.6 2 1.4 0.8 0.2

2

6

4

Length of geogrid (m)

F.S. Sliding

1.97

2.18

F.S. Overturning

4.10

4.50

Bearing Pressure

259 KN/m2

179 KN/m2

8

Slope Failure of High Embankment of Noida- Greater Noida Expressway

Noida-Greater Noida Expressway

Salient features of site • Height of embankment varies from 3m to8m • Approximately 23 km stretch • Six Lane Carriageway with Median • Side shoulders – 1.5m Paved & 1m Unpaved • Flyash covered with Good Earth

Cross-Section Proposed for NOIDAGREATER NOIDA Express Highway

Causes and types of Failure • Heavy Runoff from six lane carriageway discharged water on side slopes •Sandy Silty soil was used as cover without proper slope protection •Severe Erosion on superelevated sections • Absence of longitudinal kerb channel and chutes allowed water to drain off along slope

Types of Failure • Failures observed on both sides of slope •More pronounced on d/s side •Deep cavities were observed exposing fly ash at many locations • Undermining caused caving in of road pavement

Causes of Failure • Heavy flow of water intersected side slopes inspite of grass turfing •Deep pits in slope to provide foundation for crash barrier and electric poles •Pits were loosely backfilled

Immediate Preventive Measures • Prevention of flow of water in side slopes by providing soil filled up bags through out the slope •Filling of soil in erosion gullies •Filling of soil filled bags in deep cavities

Long Term Remedial Measures • Compaction of Side Slopes • Provision of Toe Walls • Provision of Kerb Channel • Provision of Chutes • Provision of drains in Medians • Provision of Stone Pitching along with Filter (Granular/Geotextile)

Remedial Measures

IRC Guidelines / Specifications Guidelines available on pavement construction IRC 60 ‘Tentative guidelines for use of lime fly ash concrete as pavement base or subbase’ IRC 68 ‘Tentative guidelines on cement fly ash concrete for rigid pavement construction’ IRC 74 ‘Tentative guidelines for lean cement concrete and lean cement fly ash concrete as a pavement base or subbase’ IRC 88 ‘Recommended practice for lime fly ash stabilised soil as base or subbase in pavement construction’

Conclusions • Ideally suited as back fill material for urban/ industrial areas and areas with weak sub soils • Higher shear strength leads to greater stability • Design is similar to earth embankments • Intermediate soil layers for ease of construction and to provide confinement • Side slope erosion needs to be controlled by providing soil cover • Can be compacted under inclement weather conditions • Use of vibratory rollers is preferred

 In road projects savings to the extent of 15-25 per cent can be achieved. Savings depend on cost of transportation of fly ash  Coarse ash is suitable as a fill material, finer part of the ash (fly ash) collected in dry form can be used to replace cement  Fly ash collection and handling techniques need to be improved  Use of ash for all road projects in the vicinity of thermal power plant should be made mandatory  Conservation of conventional construction materials is possible by adopting fly ash for road construction

Thank you

Use of Fly Ash for Road and Embankment Construction

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