Tunnel Design Basis Report.pdf

KOLKATA METRO RAIL CORPORATION LTD

EAST WEST METRO PROJECT CONTRACT - UG1

TUNNEL DESIGN BASIS REPORT

REPORT NO. UG1-WSA-200-NST-REP-201 REV. BC

DESIGN AND CONSTRUCTION OF UNDERGROUND SECTION FROM HOWRAH MAIDAN STATION TO WEST END OF CENTRAL STATION CONTRACT NO. UG-1

EMPLOYER

: KOLKATA METRO RAIL CORPORATION LTD

(KMRCL)

CONSULTANT

: MAUNSELL|AECOM-YEC-CES-EGISRAIL-LHPA

(MYCEL)

CONTRACTOR

: TRANSTONNELSTROY-AFCONS JOINT VENTURE

(TTAJV)

SUBCONTRACTOR : W.S. ATKINS AND PARTNERS OVERSEAS

5094704/D7003 Rev. BC

(WSA)

EAST WEST METRO PROJECT: CONTRACT - UG1 TUNNEL DESIGN BASIS REPORT UG1 Project No.

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REVISION NOTE

The following items / paragraphs are revised in this issue Item Description in brief / Para. No.

Item Description in brief / Para. No.

Section 6.2.6 revised to include reference to BS 8110 Section 6.2.7 revised to include reference to BS 8110

NOTES: Revisions are denoted as follows: a) By a vertical line in the right-hand margin against the revised text. b) By a triangle symbol for graphics, the revision number being denoted within the symbol. Revision symbols are positioned adjacent to the revision.

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CONTROL COPY DISTRIBUTION NOTE

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CONTROLLED COPY HOLDERS WILL RECEIVE THE LATEST ISSUE OF THE DOCUMENT AND THE SUCCESSIVE ISSUES. HE SHALL BE RESPONSIBLE FOR DESTROYING THE OLD REVISION OR OTHERWISE MARKING THE SAME AS “SUPERSEDED”.

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TABLE OF CONTENTS 1 INTRODUCTION ........................................................................................................................................... 6 1.1 Purpose of this Report........................................................................................................................... 6 1.2 Related Documents ............................................................................................................................... 6 1.3 Project Description ................................................................................................................................ 6 1.4 Relevant Codes & References .............................................................................................................. 7 2 TUNNEL ELEMENTS ................................................................................................................................... 8 2.1 Bored Tunnel Segmental Lining ............................................................................................................ 8 2.2 Cross Passages .................................................................................................................................... 8 2.3 Bored Tunnel to Underground Structure Interfaces .............................................................................. 9 3 MATERIAL PROPERTIES .......................................................................................................................... 10 3.1 Structural Material Properties for Permanent Works .......................................................................... 10 3.1.1 Pre-cast concrete .............................................................................................................................. 10 3.1.2 Cast In-Situ Concrete ........................................................................................................................ 10 3.1.3 Bar Reinforcement ............................................................................................................................ 10 3.2 Geotechnical Parameters .................................................................................................................... 10 4 DESIGN LOADS ......................................................................................................................................... 11 4.1 General Load Cases ........................................................................................................................... 11 4.1.1 Dead Loads (G) ................................................................................................................................. 11 4.1.2 Imposed Loads (Q)............................................................................................................................ 11 4.1.3 Hydrostatic Loads (H)........................................................................................................................ 12 4.1.4 Earth Loads (E) ................................................................................................................................. 12 4.1.5 Seismic Loads (EQ) .......................................................................................................................... 12 4.1.6 Fire Loading ...................................................................................................................................... 13 4.1.7 Internal Loading................................................................................................................................. 13 4.1.8 Dispersal on Wheel Point Loads ....................................................................................................... 13 4.1.9 Accident Load from Train Derailment................................................................................................ 13 4.2 Other Loads Considered for Segment Design .................................................................................... 13 4.3 Load Factors ....................................................................................................................................... 14 5 OVERALL STABILITY OF TUNNEL .......................................................................................................... 15 5.1 Permanent Conditions ......................................................................................................................... 15 5.1.1 Flotation Uplift due to Water Pressure .............................................................................................. 15 5.2 Temporary Conditions ......................................................................................................................... 15 5.2.1 Heave of Relatively Shallow Tunnels in Clay .................................................................................... 15 5.2.2 Tunnel Face Stability ......................................................................................................................... 15 6 DESIGN APPROACH FOR SEGMENTAL LINING ................................................................................... 16 6.1 Safety Factors For Segment Design ................................................................................................... 16 6.1.1 Ultimate Limit State (ULS) ................................................................................................................. 16 6.1.2 Serviceability Limit State (SLS) ......................................................................................................... 16 6.2 Design Approach ................................................................................................................................. 16 6.2.1 Static Lining Force............................................................................................................................. 16 6.2.2 Numerical Soil-Structure Interaction Analysis ................................................................................... 17 6.2.3 Analysis of the effects of Imposed Distortion .................................................................................... 17 6.2.4 Seismic Lining Forces ....................................................................................................................... 17 6.2.5 Analysis of the Effects of Poor Ring Build ......................................................................................... 19 6.2.6 Design of Radial Joints...................................................................................................................... 19 6.2.7 Analysis of the Effects of Jacking For Propulsion at the Circumferential Joint .............................. 19 6.2.8 Effects of Uneven Shield Shoving Loads .......................................................................................... 20 6.2.9 Grouting Loads .................................................................................................................................. 20 6.2.10 Analysis of the Handling and Stacking .............................................................................................. 20 6.3 Reinforcement Design ......................................................................................................................... 21 6.3.1 Design for Moments and Axial Force ................................................................................................ 21 6.3.2 Crack Control .................................................................................................................................... 21 5094704/D7003 Rev. 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6.3.3 Minimum Concrete Cover to Steel .................................................................................................... 21 6.3.4 Minimum Percentage of Steel Reinforcement .................................................................................. 21 6.4 Other Segmental Lining Elements ...................................................................................................... 21 6.4.1 Grooves for Waterproofing Elements ................................................................................................ 21 6.4.2 Bolts................................................................................................................................................... 21 7 TUNNEL UNDERNEATH HOOGHLY RIVER ............................................................................................ 22 8 REFERENCES ............................................................................................................................................ 23 APPENDIX 1 – Schedule of additional design codes and references ....................................................... 24

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EAST WEST METRO PROJECT: CONTRACT - UG1 TUNNEL DESIGN BASIS REPORT UG1

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INTRODUCTION 1.1

Purpose of this Report

This document provides the design basis for the tunnel works including: •

TBM bored tunnel segmental lining; and

•

Cross passages and other features.

The design of TBM tunnel segmental lining is compatible with KMRC requirements, the Contract Documents and Specification and conditions in the local environment. 1.2

Related Documents

This report should be read in conjunction with the following documents: -

Contract Specifications and Drawings

-

Reports Geotechnical Reports •

Geotechnical Assessment Report

UG1-WSA-300-NGT-REP-003

Design Reports • 1.3

Structures Design Basis Report

UG1-WSA-000-ENG-REP-001

Drawings – Tender submission drawings and/or Preliminary Design Drawings

Project Description

The Kolkata Metro Rail Corporation (KMRC) has issued tenders for the construction of East West Metro Project including UG1 and UG2 sections. The Contract UG1 comprises approximately 3.7km of railway tunnels and 3 stations with the following major elements: •

Howrah Maidan Station;

•

TBM tunnel between Howrah Maidan Station and Howrah Station (east bound and west bound);

•

Howrah Station;

•

TBM tunnel between Howrah Station and Mahakaran Station (east bound and west bound) underpassing the Hooghly River;

•

Vent shaft and connecting adits at midway between Howrah and Mahakaran Station

•

Mahakaran Station

•

TBM tunnel between Mahakaran Station and Central Station (by others)

The TBM tunnels will be constructed between proposed cut and cover stations and no additional temporary shafts are required.

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Relevant Codes & References

In addition to the Contract Requirements, the proposed underground structures will be designed in accordance with IS-456:2000 and IRS-Bridge Rules for Loading (Ministry of Railways). IRC-6:2000 will be used to obtain the highway loading above and adjacent to the proposed underground structures. Other appropriate Indian Standard/Code (IS, IRS, IRC, NBC) may also be referenced to, if better definition is given in that standard, or as expressly required by the Outline Design Specification. International standard/codes e.g. British Standard, Eurocodes, AASHTO, ASTM, CIRIA report may be used if they provide more detailed design checking approaches. Additional proposed structural design codes and references are detailed within this report are summarized in Appendix 1.

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TUNNEL ELEMENTS 2.1

Bored Tunnel Segmental Lining

The pre-cast concrete segmental lining forms part of the permanent support of the tunnel and is installed inside the shield of the Tunnel Boring Machine (TBM), as the tunnel excavation progresses. The TBM shield will be larger than the lining outer diameter. The void between the ground and the tunnel lining will be continuously filled with grout from the shield tail. The segment lining consists of five large segments plus one key segment for each ring. The lining thickness is 275mm with internal diameter of 5.55m. The same universal segment ring will be used for the whole contract in the following sections: •

Running tunnels between Howrah Maidan Station and Howrah Station (east bound and west bound);

•

Running tunnels between Howrah Station and Mahakaran Station (east bound and west bound); and

•

Running tunnels between Mahakaran Station and the perimeter wall of Central Station (east bound and west bound.

The segments are bolted together during erection inside the tunnel shield, with bolts on the circumferential joint of each ring edge and bolts on the radial joints of each ring. The bored tunnel waterproofing is provided by a hydrophilic seal and EPDM (Ethylene Propylene Diane Monomer) gasket on the segment circumferential joints. The hoop load induced into the bored tunnel as a result of the ground water pressure and soil loads will be sufficient to compress the gaskets to prevent groundwater intrusion in combination with the hydrophilic swelling properties. Gaskets on the circumferential joints will be compressed by the TBM jacking pressure and locked by the bolts connecting segments. No membranes will be used due to the tunnelling construction method. 2.2

Cross Passages

Six cross passages are proposed to connect the running tunnels for the purpose of emergency egress and at the Vent Shaft as ventilation adits to the running tunnels. The cross passages will be constructed by mining (NATM) excavation and temporary support using reinforced shotcrete linings and lattice girders. The design of the temporary support will encompass issues such as: •

Temporary face stability and support;

•

The need for ground treatment and/or pre-support measures;

•

Control of groundwater; and

•

Excavation and support sequencing to limit ground movements.

These issues will be developed in the relevant Design Reports. Design analysis will be undertaken using analytical and numerical methods. In order to facilitate the opening of the running tunnel segmental lining for cross passage connection, a temporary support frame of steel ring beams and beams will be adopted. This will be designed as a structural frame to accommodate tunnel lining loads that will develop during breaking of the tunnel wall. The temporary steel members and permanent steel jamb frame to be placed in the tunnel wall will be designed in accordance with relevant steelwork codes compliant with the Contract specifications. 5094704/D7003 Rev. BC


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The permanent support lining to the cross passages will comprise non-circular cast in-situ concrete lining. The design of the lining will be undertaken using numerical modelling methods and detailed in line with the Structures Design Basis Report. 2.3

Bored Tunnel to Underground Structure Interfaces

The bored tunnel will interface with station structures. For most cases the segmental tunnel lining will be placed during TBM operations and the lining at the station diaphragm wall headwall will be encapsulated into a cast in-situ reinforced concrete joint block. Where the TBM drives terminate at the Central Station headwalls, it is proposed that the TBM shield will be abandoned in-situ (i.e. removing all other TBM components) and the tunnel completed between the segmental lining rings and the headwall by a cast in-situ lining with the abandoned shield incorporated within the lining. For both of the above cases, the joint details will be designed to provide: •

Accommodation of necessary articulation if needed;

•

Waterproofing details including secondary measures; and

•

Capacity to carry soil, water and other loads including seismic impacts.

These details will be developed in the relevant Design Reports and the design will be governed by the criteria given in the Structures Design Basis Report.

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MATERIAL PROPERTIES 3.1

Structural Material Properties for Permanent Works 3.1.1

Pre-cast concrete

The material properties of pre-cast concrete lining are listed below: Characteristic strength, fcu

50 N/mm2 (min)

Modulus of elasticity, Ec (short-term)

35 355 N/mm2

Modulus of elasticity, Ec (long-term)

16 836 N/mm2 (Note 1)

Poisson’s ratio, v

0.2

Moment of inertia, Ir

0.000878 m4 (Note 2)

Note 1: The long–term modulus of elasticity of concrete is calculated with the consideration of creep effect. The calculation method and coefficients are based on IS 456:2000 Clause 6.2.5.1. Note 2: The lining stiffness is reduced according to the Muir Wood [Ref. 9] approach to account for the effect of radial joints. This is based on the number of joints for each ring and the reduction of lining thickness at joints: Ir=Ij + (4/n)2 x I Where,

Ij is the moment of inertia at the joint; I is the moment of inertia for the nominal lining thickness: and n is the number of segments for each ring.

3.1.2

Cast In-Situ Concrete

For permanent cast in-situ elements, structural materials will be as those described in the Structures Design Basis Report. 3.1.3

Bar Reinforcement

The bar reinforcement for segments are high yield steel deformed bar and the material properties are listed below:

3.2

Characteristic strength, fy

500 N/mm2

Modulus of elasticity, Es

200 000 N/mm2

Geotechnical Parameters

The geotechnical parameters including groundwater are provided in the Tunnel Geotechnical Assessment Report UG1-WSA-200-NGT-205.

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DESIGN LOADS This section summarises general loads to be considered for the design of bored tunnels and non-TBM tunnels. If for particular structures or conditions where loads deviate from those specified herein, the related assumptions will be given in the respective Design Reports. 4.1

General Load Cases

The loads specified in this Section are characteristic or nominal loads in accordance with BS 8110, Part 1, Ref [1] and are categorised as follows: •

Dead Load (G);

•

Imposed Load (Q);

•

Hydrostatic Load (H); and

•

Earth Load (E).

These cases are described below. 4.1.1

Dead Loads (G)

For the calculation of dead loads the following unit weights (γ) apply: Table 3-1: Unit weight of materials Material

Unit Weight (kN/m3)

Reinforced concrete

24.0 (Refer IS 875 Part 1, average density of RC with 2% steel)

Mass concrete

23.5

Steel

77

Water

10

4.1.2

Imposed Loads (Q) 4.1.2.1

General Surcharge Load (Q1)

A minimum surcharge of Q1 = 50 kPa acting at ground surface level as per Section 2.7.5(e) of Volume 4 of the Contract Specifications is considered. This shall make allowance for existing or future buildings for which detailed information currently is not available. The surcharge from existing buildings will be calculated and added where the total load from the building is greater than 50kPa as per the Structures Design Basis Report. 4.1.2.2

Live Loads from Road Traffic (Q2)

Tunnel structures under highway roads shall be designed for Q2 = 20 kPa surcharge for highway loadings. This is equivalent to the vertical load produced from Class AA loading as per Clause 2.7.5(b) of the Contract Specifications and as defined in IRC:6-2000, assuming the pressure from the wheels are spread over minimum 2m thick backfill. 5094704/D7003 Rev. BC


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Wheel from train (Q3)

The railway loading applied to the structures shall be as per “Modern Rolling Stock”. The standard gauge is 1435mm. Maximum axle load of the train, P = 160kN, see the diagram below for the details of loading configuration. The type and position of the vehicle will be chosen to produce the most adverse effect on the structure.

The loading from maintenance vehicles and low loaders carrying equipment required along the route will not be of a magnitude to be critical for the design. 4.1.3

Hydrostatic Loads (H)

The upper or lower bound of the groundwater level should be taken into account in deriving hydrostatic loads, whichever is more critical for the structure or condition being considered. 4.1.4

Earth Loads (E) 4.1.4.1

Soil Overburden / Vertical Earth Pressure (E1)

In general, full overburden loads will be considered for the design of permanent tunnel structures. For temporary structures the earth pressure considered may be less than the full overburden. Situations that justify the assumption of less than the full overburden pressure will be explained in the respective Design Reports. 4.1.4.2

Lateral Earth Pressure (E2)

For permanent structures in general, lateral earth pressure are derived assuming at-rest condition. Due to the nature of a structure (e.g. shafts or temporary structures) reduced lateral pressure may be applicable. Related assumptions will be presented in the respective Design Reports. 4.1.5

Seismic Loads (EQ)

Refer to Section 6.2.4. 5094704/D7003 Rev. BC


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Fire Loading

Tunnel linings will be designed to satisfy the minimum sectional requirements to achieve a 4 hour Fire Resistance Period (FRP), in accordance with NFPA 130-2007, as specified in the Outline Design Specification. For a 4 hour FRP rating, cover to steel bar reinforcement will not be less than •

25mm as defined in IS 1642:1989 Table 8 for the tunnel lining and

•

75mm as defined in IS1642:1989 Table 13 for the lintel beam in the tunnel lining above the entrance to the cross passage.

Additional stresses in the tunnel lining will be assessed according to BS8110, Part 2 [Ref: 1]. 4.1.7

Internal Loading

The effects of internal loads, especially loads imposed by services fixed to the tunnel walls and roof will be taken into account in the segmental lining design and/or cast insitu tunnel linings. 4.1.8

Dispersal on Wheel Point Loads

Dispersal on wheel point loads follows the approach as outlined in Section 14.8 and Appendix C of the Structures Design Basis Report Ref: UG1-WSA-000-ENG-REP001 4.1.9

Accident Load from Train Derailment

Within the bored tunnel, the segmental ring will be designed to take the full impact load, which will be resisted by the passive resistance of the ground behind the wall. Derailment loading shall be applied to adjacent structural elements in accordance with Cl 3.5.2 ACI 358.1R-92 (The American Concrete Institute technical design standard, Analysis and Design of Reinforced and Prestressed Concrete Guideway Structures). The horizontal derailment load shall be taken as 50% of the maximum car weight: for the most heavily loaded car which has 4 axles of 160 kN each, this amounts to a nominal force of 320 kN applied over a 5m horizontal length for the SLS case, where the serviceability requirement is that there should be no permanent damage and the structure should remain within the elastic range in accordance with IRS bridge rules. 4.2

Other Loads Considered for Segment Design

Additional load cases to be considered are: •

Load due to compression of EPDM gaskets and hydrophilic seals;

•

Demolding, stacking and handling;

•

TBM shoving/ Ram Load (Q4) for a maximum TBM shoving force of 42,560kN.

•

Tail void grouting and secondary grouting; (Q5).

Further comments on assessment of load cases Q4 and Q5 are given in the next sections.

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Load Factors

General load factors (ULS – Ultimate Limit State, SLS – Serviceability Limit State) as outlined below will be considered for the design of bored tunnels in additional to Contract Document Volume 4 Section 2.7.10. As per IS4651, Part 4, Table 1 Planning and Design for Ports and Harbours a load factor of 1.0 is taken for SLS design checks. Table 3-2: Load factors Loading Condition

Ultimate Limit State

Serviceability Limit State

Dead Load

1.4

1.0

Imposed Load

1.4

1.0

Earth Load

1.4

1.0

Hydrostatic Load

1.4

1.0

Ram Load

1.4

N/A

Handling Load

N/A

1.0

Grout Load

1.4

N/A

Derailment Load

1.4

1.0

Note that for the purposes of numerical soil-structure interaction analysis, partial safety factors (ULS factor =1.4, SLS factor =1.0) will be applied to computed bending moment and forces for use in structural design, rather than input into initial parameters and load cases.

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OVERALL STABILITY OF TUNNEL 5.1

Permanent Conditions 5.1.1

Flotation Uplift due to Water Pressure

Where tunnels are relatively shallow, they should be checked for flotation due to differential water pressure as follows: Overall safety factor =

R / U ≥ 1.2

Where: R …. Restraining force calculated by weight and shear resistance of soil U …. Net uplift force considering weight of tunnel In deriving the restraining and uplift force, the following partial safety factors need to be considered: Table 4-1: Partial safety factors for uplift due to water pressure

5.2

Self weight of tunnel

1.05

Self weight for shafts or other structures

1.1

Average shear resistance along planes of failure

2.0

Average weight of ground above tunnel

1.15

Temporary Conditions 5.2.1

Heave of Relatively Shallow Tunnels in Clay

Where applicable for relatively shallow tunnels in clay, checking for heave due to shear failure of the ground at tunnel invert level (for example, for mining operations) will be undertaken following the method derived from the base heave analysis after Bjerrum & Eide (1956) [Ref: 5]. Where: Overall safety factor:

≥ 1.0 when surcharge is applied ≥ 1.2 when surcharge is not considered

For partial safety factors for soil shear strength and unit weight, refer to the table above. 5.2.2

Tunnel Face Stability

For TBM bored tunnelling works, the tunnel face stability is to be managed through the application of appropriate face pressure. Definition of appropriate face pressure magnitude and use will be dealt with in later design stages. For cross passage mining works the tunnel face stability during excavation is of particular concern. Face stability will be evaluated on the basis of ground parameters adopted excavation and temporary support methods. Where ground conditions are relatively poor and instability or severe ground movement is likely then mitigation works such as ground treatment or pre-support measures will be developed. Definition of appropriate measures will be dealt with in later design stages. 5094704/D7003 Rev. BC


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DESIGN APPROACH FOR SEGMENTAL LINING 6.1

Safety Factors For Segment Design 6.1.1

Ultimate Limit State (ULS)

Segments are designed for the ULS in accordance with IS-456:2000. Partial safety factors for loads and materials are in accordance with the Contract documents, IS456:2000 or BS8110 [Ref: 1] where relevant. Where appropriate for particular structures or conditions, different partial safety factors may be adopted as specified in this design statement. For specific partial safety factors for segment design refer Section 4.3. In addition, the following partial safety factors are used for specific conditions: Table 5-1: Load factors for Ultimate Limit State Design Load factor on TBM shove loads for normal operations

1.4

Maximum expected TBM shove thrust on single rams

1.4

6.1.2

Serviceability Limit State (SLS)

Segments will be checked for serviceability in accordance with IS-456:2000, BS8110 and BS 8007 [Ref: 1 and 6]. In general, serviceability calculations such as for crack control or deflections are based on service loads (i.e. load factor = 1.0) Tensile stresses due to demoulding, stacking, rotating, transport and handling for erection of ring are to be checked as per the load factors below. The related safety factors are as follows: Table 5-2: Load factors for Serviceability Limit State design

6.2

Dynamic factor for demoulding, stacking, rotating, transport, handling (as per Contract document Volume 4 Section 2.7.10(d))

5.0

Material safety factors for concrete in tension

1.5

Design Approach

This section provides a basic summary of the approaches and assumptions and covers various aspects of design and detailing of reinforced concrete segments. 6.2.1

Static Lining Force

The closed form analysis model after Duddeck & Erdmann [Ref: 8] or similar internationally recognised method, such as the Curtis-Muir Wood method [Ref: 9, 10], is used for the structural analysis of the segment lining. A full bond between the lining and the subsoil is assumed. Calculations will be carried out for the average effective unit weight (γ‘av) of soil, considering the soil layers and groundwater table. The effect of differential hydrostatic pressure along the circumference of the tunnel will be considered in the analysis. This is based on a general plane frame analysis that will be carried out for varying soil stiffness and differential hydrostatic load.

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Numerical Soil-Structure Interaction Analysis

For specific locations, it may be more appropriate to use numerical soil-structure interaction analysis rather than analytical calculations alone. In these cases, for example where deep foundations impart localized loading to the tunnel lining, then numerical analysis will be used. Numerical analysis will be undertaken using PLAXIS version 9. A volume loss of 1.5% is assumed for the PLAXIS analysis. This is conservative compared to typical values for earth pressure balance tunnelling with tail-skin grouting in soft clay. 6.2.3

Analysis of the effects of Imposed Distortion

The maximum allowable deflection of the tunnel lining is 25mm on radius of the tunnel. The induced bending moment by applying this distortion is derived by using the method of Morgan [Ref 14] for jointed lining cases with reduction of lining moment of inertia based on the recommendation by Muir Wood [Ref. 9]. The predicted bending moment coupled with minimum thrust force will be input for reinforcement calculation. 6.2.4

Seismic Lining Forces

Kolkata is considered to be in seismic Zone 3 in accordance with Annex E of IS-1893: 2002, giving a Zone Factor, Z = 0.16g, corresponding to the Maximum Considered Earthquake (MCE) which is the largest conceivable earthquake within the tectonic region as defined by the code. According to the clause 6.1.3 of IS-1893: 2002, the design methodology adopted by that code will ensure that the structures will possess at least a minimum strength to withstand a DBE event “without significant structural damage” and an MCE event “without collapse”. The design of tunnels to resist seismic loads is not explicitly covered by the Indian Standards; hence reference is made to internationally recognised design methods from published literature. In accordance with IS-1893:2002, the horizontal seismic accelerations corresponding to the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE) are 0.16g and 0.08g respectively. The “Free-field racking deformation” method as elaborated in Hashash et al [Ref 17] has been adopted for the design. The method assumes the structure will be racked by the soil surrounding it during an earthquake, with the degree of racking dependant upon the relative shear stiffness of the structure to the soil mass it replaces, and the free-field soil deformation profile. The procedures for design are detailed below: 1. Preliminary design and member sizing is based upon static design (G, Q, E, H). Two numerical models shall be developed, one for the DBE and one for the MCE seismic events, with the following section properties: DBE (0.08G) 1 1.0EI Notes: 5094704/D7003 Rev. BC

MCE (0.16G) 2

0.70EI


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Stiffness values are the same as for the static, short-term model 70% reduction of EI due to cracking of a member subject to compression.

2. The free field deformation of the soil during a seismic event is derived using the SHAKE2000 software. The design inputs include ground motions obtained from the SHAKE2000 software library and from publically available ground motion libraries. The latter include strong ground motions from the Chamoli (1999), Diphu (1988) and Burma (1995) events. The input data includes soil profile, ground acceleration due to 0.08g (DBE) and 0.16g (MCE) and dynamic shear modulus derived from the ground investigation. 3. Obtain Lining-soil racking ratio (R) for the structures and the soil mass by the equation.

R=±

Δd lining 4(1 − υ m ) = (α + 1) Δd free− field

, where Δdlining = lining diametric deflection Δdfree-field = free-field diametric deflection νm = Poisson’s ratio of the soil medium α = coefficient used in calculation of lining-soil racking ration of circular tunnels dependent on whether slip is permitted between the soil medium and the tunnel lining. R is used to derive the lining diametric deflection Δdlining for input into thrust and bending moment expressions below. 4. The circumferential thrust and bending moment in the lining as a function of the angular location of the tunnel lining is obtained using the expressions by Hashash et al [Ref 17]. 5. Superimpose the seismically induced thrust and bending moment distributions to the results obtained from the numerical model. The circular tunnel shall also be designed to resist vertical components of the seismic motion, with the vertical component, Av, taken as 2/3 of the horizontal component, Ah. Where two or three component motions are considered, then these shall be combined in accordance with Section 6.3.4 of IS-1893: 2002. Since the permanent structure is designed for the ‘at rest’ condition’, no net additional dynamic loading need be applied to the structure either before or after the seismic event. 6. The following design combinations shall be considered for the section design under seismic load: For the DBE case, the load factor of 1.4 is applied in accordance with: 1.4 x (1.0 (G + Q) + 1.0E + 1.0 H +/- 1.0 EQH +/- 1.0 EQV) The MCE is an extreme event and is not explicitly a design requirement of the Indian code. Hashash et al [Ref. 17] recommend that for the MCE event, the partial safety factors for all loads should be unity. 1.0 (G + Q) + 1.0 E + 1.0 H +/- 1.0 EQH +/- 1.0 EQV

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Note that combined DL and LL allows for the 50kPa minimum surcharge at the ground surface for both DBE and MCE. 7. If the results from (7) show that the structure has adequate capacity then the design is considered to be satisfactory. 6.2.5

Analysis of the Effects of Poor Ring Build

The key construction tolerances for ring build are a maximum of 25mm on radius of ring due to ovalisation and the limitation on stepping of segments at the circumferential and radial joints (5mm). Poor ring build can induce significant loading and therefore, the following are checked: • Whether the radial joints remain closed or open (birds-mouth) as a result of the diametrical ovalisation taking into account the minimum predicted imposed ground and groundwater loads; • The induced bending moment as a result of thrust eccentricity across radial joints due to the reduced bearing area due to birds-mouthing. The induced bending moment is added to the maximum bending moment from continuum analysis for the reinforcement design; • The induced tensile stresses (bursting) induced as a result of thrust eccentricity across radial joints due to the reduced bearing area due to birdsmouthing (method as described for jacking loads); and • The increased loading to both radial and circumferential segment surfaces as a result of stepping. 6.2.6

Design of Radial Joints

Due to the width of the bearing faces being less than the lining section thickness, transverse tensile stresses occur at the joints. This bearing area is further reduced where joint rotations occur due ring deflection or ring building defects, causing increasingly concentrated loads. The joint design for splitting tensile effects due to concentrated loads are based on BS 8110 [Ref 1]. Steel link bars will be placed between the main reinforcement to counter tensile forces beyond the capacity of the concrete as required. 6.2.7

Analysis of the Effects of Jacking For Propulsion at the Circumferential Joint

The jacking loads imposed by the hydraulic propulsion jacks onto the leading edge circumferential joint of the segmental lining ring are a significant load case. These loads are in the longitudinal direction. Due to their localisation and jack eccentricity to the lining (possibly exacerbated by ring build defects), significant additional stresses may be induced in the lining. Particular attention is given to the induced tensile stresses that may cause cracking and spalling. Reinforcement of the segment to accommodate these stresses will be included as required.

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The effect of these forces will be assessed using BS 8110 [Ref 1]. The required reinforcement to accommodate tension under compressive loads and bending moment will be determined. TBM shoving loads acting at circumferential joints cause bursting stresses, as the bearing width of the rams and joint packing are less than the segment thickness. 6.2.8

Effects of Uneven Shield Shoving Loads

Additional flexure and torsion may generally be induced on segments, when shoving loads are not equally distributed, due to steps along the circumferential joints. In order to minimise damage during shoving, accurate ring build is crucial. The use of joint packing will further help to mitigate such effects by reducing load concentration. 6.2.9

Grouting Loads 6.2.9.1

Tail Void Grouting

An ultimate grouting pressure of 1.0 bar (Pmax) above hydrostatic pressure acting radially on the segment will be applied considering a load factor of 1.4. The load is considered to be applied fully around the tunnel. 6.2.9.2

Secondary Grouting

The lining shall generally be designed to resist a maximum grout pressure equivalent to the maximum water pressure plus 1.0 bar (100kPa) considering a load factor of 1.4. 6.2.10 Analysis of the Handling and Stacking The segment is checked for the effects of handling using a dynamic factor (Df = 5) to account for lifting operation. Stacking loads are assessed based on the following assumptions: • The segments are stacked in a convex curve-down arrangement or reversed curve-up arrangement with soft wood packing blocks at the quarter points; • The concrete has achieved the minimum strength of 10MPa when stacked; • The maximum number of segment for each stack is 6, which is for one ring; and • The maximum offset for the packing blocks is 100mm. Segments will be designed for stresses during demoulding, stacking and erection of the segments. Stresses are generally calculated by elastic methods to ensure that the modulus of rupture of the unreinforced concrete is not exceeded and thus the segments remain uncracked. Calculation of the allowable flexural strength of concrete fcr, shall be obtained from the compressive strength using the following expression from IS456:2000.

f cr = 0.7 f ck (MPa) where fck = characteristic cube compressive strength of concrete (MPa)

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Reinforcement Design 6.3.1 Design for Moments and Axial Force Main reinforcement will be designed for load cases and combinations as defined in Section 4. The required reinforcement is derived for the Ultimate Limit State in accordance with IS-456:2000. 6.3.2 Crack Control The calculated maximum crack width should not exceed 0.20mm for permanent loading condition. Crack widths are calculated in accordance with IS-456:2000. 6.3.3 Minimum Concrete Cover to Steel Given the anticipated exposure conditions, the minimum concrete cover to steel reinforcement shall be 40mm on the extrados and 40mm on the intrados.. For the section of tunnel beneath the river, the minimum cover to steel reinforcement shall be 50mm on the extrados. Concrete mix design will consider and address the aggressiveness of the ground conditions the segmental lining and other structural concrete will be exposed to. 6.3.4 Minimum Percentage of Steel Reinforcement Wherever reinforcement is structurally required, minimum reinforcement according to IS-456:2000 shall apply.

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Other Segmental Lining Elements 6.4.1 Grooves for Waterproofing Elements Grooves for gaskets and seals are designed to seal under the worst case conditions, making allowance for the casting inaccuracies and building errors. 6.4.2 Bolts Bolts are used to tie adjacent segments and rings together. The bolts are designed to keep the sealing gaskets compressed, when part of the shield thrust is relieved during erection of the rings. Further behind the shield, the friction between lining and ground is sufficient to keep the gaskets compressed.

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TUNNEL UNDERNEATH HOOGHLY RIVER Bored tunnelling using the EPB TBM method below the Hooghly River presents some particular issues that will be addressed in detailed design and construction: •

Design checking to anticipate any risk of flotation of the tunnels – this has been checked and it is considered that this is not a significant risk;

•

Design of TBM face pressures to be applied – it is particularly important to recognise the required pressure changes when passing beneath the river banks so as to ensure stability but to avoid overpressure;

•

Construction planning should accommodate the risk of encountering buried obstacles (although this appears unlikely); and

•

Contingency measures should be planned in the event of having to undertake repair works (i.e. obstacle removal, repair to cutterhead damage, repair to major TBM components, etc) from within the cutterhead using relatively high compressed air pressures.

These issues will be developed through the relevant Design Reports.

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REFERENCES [1] BS8110 (1997): “Structural use of concrete. Code of practice for design and construction”. British Standard Institution [2] BS4449 (1997): “Specification for carbon steel bars for the reinforcement of concrete”. British Standard Institution [3] EN10025-1 (2004): “Hot rolled products of structural steels – Part 1: General technical delivery conditions”. British Standard Institution [4]

GAR (Geotechnical Assessment Report) – Underground Section.

[5] Bjerrum L. and Eide O. (1956): “Stability of strutted excavations in clay”. Geotechnique 6. [6] BS8007 (1987): “Code of practice for design of concrete structures for retaining aqueous liquids”. British Standard Institution [7] Meyerhoff G. (1951): “The ultimate bearing capacity of foundations”. Geotechnique 6 vol.2 No. 41. [8] Duddeck H. and Erdmann J. (1982): “Structural design models for tunnels”. Proceedings of Conference Tunnelling ’82, pp 83-91, UK [9] Muir Wood, A.M. (1975). “The circular tunnel in elastic ground”. Geotechnique 25, No. 1, 115 – 127. [10]

Curtis, D.J. (1976) “Discussion”. Geotechnique 26, 231 - 237.

[11] Wang, J.N., (1983): “Seismic design of tunnels: A simple state-of-the-art design approach” Monograph 7, William Barclay Parsons Fellowship, USA. [12] Monsees J.E. and Richard D.P. (1994): “Seismic Design of Underground Structures”. 1st Conference Egyptian Society for Earthquake Engineering, Cairo [13] Eurocode 2 (1992): “European Pre-Standard pr ENV 1992-1-12, Eurocode 2, Design of Concrete Structures – Part 2, Plain or Lightly Reinforced Concrete Structures”. [14] Morgan H. D. 1961. “A contribution to the analysis of stress in a circular tunnel”. Geotechnique, Vol. 11, p37. [16] Janβen P. (1983): “Tragverhalten von Tunnelausbauten mit Gelenktubbings (Structural Behaviour of Segmental Tunnel Linings with Flexible Joints)”. Hashash, M.A., Hook, J.J., Schmidt, B. and Yao, J.I. (2001): “Seismic design and analysis of underground structures”. Tunnelling and Underground Space Technology Vol. 16 p 247-293.

[17]

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APPENDIX 1

APPENDIX 1 – Schedule of additional design codes and references

BS8328-1

Part 1: Guide to specifying concrete

BS 8110

Structural use of Concrete Code of Practice for Design and Construction

BS 5950

Structural Use of Steelwork in Building:

BS 8007

Design of Concrete Structures for Retaining Aqueous Liquids

BS EN 1993-1-1:2005

Eurocode 3: Design of steel structures — Part 1-1: General rules and rules for buildings

CIRIA C660

Early-age Thermal Crack Control in Concrete

BRE SD1 2005

Concrete in Aggressive Ground

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Tunnel Design Basis Report.pdf

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