analysis & design of cut & cover tunnel in high seismic...

ANALYSIS & DESIGN OF CUT & COVER

TUNNEL IN HIGH SEISMIC ZONE

Prashant Kumar#1

, Nishant Kumar#2

, Sunil Saharan#3

#Department of Civil Engineering

1,2,3, College of Engineering Roorkee

1, Sharda University

23

[email protected]

[email protected]

[email protected]

Abstract— In today’s world, buried structures are used for a variety of purposes in many areas such as transportation, underground

depot areas, metro stations and water transportation. The serviceability of these structures is crucial in many cases following an

earthquake; that is, the earthquake should not impose such damage leading to the loss of serviceability of the structure. This paper

presents seismic response of highway tunnels through a case study on Cut & Cover Tunnel, which is well documented and subjected to

earthquake. In the analyses, the seismic response of a section of the tunnels is examined with 2-D finite element model and 3-D finite

element model. 2-D & 3-D FEM model are analyzed & interpretation of stresses to get final design forces and comparison of analysis

results between 2-D & 3-D FEM model has been done. It is observed that there is little variation between 2-D & 3-D FEM Displacement

& Moment results except for the load cases which includes seismic force.

Keywords— Seismic Analysis, Cut & Cover Tunnels, Finite Element Analysis, Soil-Structure Interaction.

I. INTRODUCTION

Underground structures are becoming increasingly popular because of the fast growth of the population and

decreasing of the ground space, particularly in urban areas all over the world including high seismic risk

zones. Accordingly, in many cases the design of such structures must incorporate not only the static loading

but the earthquake loading as well. Underground structures have distinct features that make their seismic

behaviour radically different from surface structures in general, most notably due to (i) their complete

enclosure in soil or rock, and (ii) their significant length (i.e. tunnels) [2] .In underground structures, the

response is mainly dominated by the surrounding soil medium rather than the inertial properties because of

the very large inertia of the ground with respect to that of the structure. Main differences of the seismic

response of underground structures from those of the surface structures are that the seismic effect is

controlled by the deformation imposed on the structure by the ground, not by the forces or stresses and the

inertia of the surrounding soil is much larger relative to the inertia of the structure for most underground

facilities. Therefore, the free-field deformation of the ground and its interaction with the structure are the

main interests in the seismic design of underground structures. The Construction of 4 lane divided

carriageway from Udhampur to Banihal section of NH-1A, in the State of Jammu and Kashmir consists of

number of tunnels that are proposed on this stretch (Nashri – Chennani Tunnel, Chanderkote bypass Tunnel

etc). The longest tunnel is Nashri – Chennani Tunnel (about 9 km long). The proposed design of cut and

cover tunnel is part of Chanderkote bypass tunnel. The total tunnel length is about 888m and it is proposed

for north bound traffic for Srinagar. The initial 115m length is proposed as cut and cover tunnel due to

shallow rock cover. Remaining length is underground.

The Cut& Cover part of Chanderkote bypass tunnel was studied in this project. The description of tunnel is

given below:-

Finished size of the cut & cover tunnel and southern portal is shown in fig.1.

Alochana Chakra Journal

Volume IX, Issue V, May/2020

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Fig.1. Cut & Cover Tunnel and South Portal – Cross-section (AUTO-CADD)

Table 1. Details of Cut & Cover tunnel

Height of Tunnel 10.6 m

Width of Tunnel 11.6 m

Carriageway Width 7.5 m

Radius 5.1 m

The aim of the study is to evaluate the seismic forces acting on the tunnel using WANG racking method

of deformation, to analyse and design the cut & cover tunnel using 3D FEM STAAD Pro model and to

verify the 2D FEM results with 3D FEM analysis

II. FINITE ELEMENT MODELLING

The Plate/Shell finite element is based on the hybrid element formulation. The element can be 3-noded

(triangular) or 4-noded (quadrilateral). If all the four nodes of a quadrilateral element do not lie on one plane.

It is advisable to model them as triangular elements. The thickness of the element may be different from one

node to another. ―Surface structures‖ such as walls, slabs, plates and shells may be modelled using finite

elements. The following geometry related modelling rules are followed while using the plate/shell element.

1. The program automatically generates a fictitious, centre node ―O‖ at the element centre.

2. While assigning nodes to an element in the input data, it is essential that the nodes to be specified

clockwise. For better efficiency, similar elements should be numbered sequentially.

3. Element aspect ratio should not be excessive. They should be on the order of 1:1 and preferably less

than 4:1.

4. Individual elements should not be distorted. Angles between two adjacent elements sides should not

be much larger than 90 and never larger than 180.

During the generation of element stiffness matrix, the program verifies whether the elements are same as the

previous one or not. If it is same, repetitive calculations are not performed. The sequence in which the

element stiffness matrix is generated is the same as the sequence in which elements are input in element



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incidences. Loads are specified in the STAAD model. Design is based on the most adverse combination of

probable load conditions. However, only those loads are selected which have reasonable probability of

simultaneous occurrence. Loads taken into consideration are Self-weight (SW) 2D/3D, Superimposed dead

load (SIDL) 2D/3D, Earth Pressure (EP) 2D/3D, Water Pressure and Buoyancy (WP) 2D/3D, Racking Force

(RF) 2D/3D, Live Load (LL) 2D/3D. Analysis of structure was performed for following load combinations

SW + EP = Load Case 101,201,301

SW + SIDL + EP= Load Case 102,202,302

SW + SIDL + EP + SO= Load Case 103,203,303

SW + SIDL + EP + SO + LL= Load Case 104,204,304

SW + SIDL + EP + SO + LL + RF= Load Case 105,205,305

SW + SIDL + EP + WP= Load Case 111,211,311

SW + SIDL + EP + WP + SO= Load Case 112,212,312

SW + SIDL + EP + WP + SO + LL= Load Case 113,213,313

SW + SIDL + EP + WP + SO + LL + RF= Load Case 114,214,314

Following are the Indian Standards used in the analysis

IRC 6:2014 Standard specifications and code of practice for road bridges. [11]

IRC: 112-2011, ―Code of practice for concrete road bridge‖.[12]

IS: 456-2002, ―Code of Practice For Plain And Reinforced Concrete‖.[7]

IS 1786 (2008): High strength deformed bars and wires for concrete reinforcement.[13]

IS 1893 PART 1 - Criteria for earthquake resistant design of structures.[8]

EN 1992-1-1 (2004) – Design of concrete structures – Part 1-1.[9]

Seismic design of tunnels-Jaw Nan Wang. [6]

The grade of concrete is M30 and density of concrete is taken as 25kN/m3conforming to IS: 456. The grade

of steel is of Fe500 conforming to IS: 1786. Density of the reinforcement is taken as 7850 kg/m3. For the

type of geological conditions available at site, density of the soil assumed as 26kN/m3 and Poisson’s ratio of

the surrounding rock was assumed as 0.25. Permissible (allowable) stresses for M30 grade of concrete is

obtained from Cl. 12.2.1, IRC 112 [12] and the mean value of axial tensile strength of concrete is obtained

from Table 3.1 of Euro code EN 1992-1-1:2004 [9]. STAAD Pro V8i, finite element software was used for

the purpose of the structural analysis. Thick shell element model of 10m length was developed for the

structure. Irregular meshing has been done to cater the typical shape of the structure. Fig. 2 presents thick

shell finite element model of the structure.

Fig. 2. Thick shell model of Southern Portal (STAAD Pro V8i.)



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III. RESULT AND DISCUSSION

Compressive Stress results are summarized in table 2 and compared with the prescribed limits of stresses,

recommended by IS 456: 2000 & IRC 112:2011.

Table 2. Maximum compressive stress in concrete

S.No. Component Governing Load Case Max. Compressive

stress (MPa) in concrete

1 Top slab top SW+SIDL+EPS+WP+SO+LL+RF 14.33

2 Top slab bottom SW+SIDL+EP+SO+LL+RF 7.33

3 Wall outside SW+SIDL+EP+SO+LL+RF 12.83

4 Wall inside SW+SIDL+EP+SO+LL+RF 12.03

5 Base slab top SW+SIDL+EP+SO+LL+RF 7.43

6 Base slab bottom SW+SIDL+EPS+WP+SO+LL+RF 6.71

It can be observed from the results presented in Table 3 recommended by IS 456:2000 & IRC 112:2011 that

maximum compressive stresses are well within the permissible stresses. Crack-width results are summarised

as below (Maximum permissible crack width is taken as 0.2mm).

Table 3 Maximum crack width results

S. No. Component Governing Load Case Max. crack

width(mm)

1

Top slab top SW+SIDL+EPS+WP 0.058

2 Top slab bottom SW+SIDL+EP+SO 0.06

3 Wall outside SW+SIDL+EP+SO 0.12

4 Wall inside SW+SIDL+EPS+WP 0.19

5 Base slab top SW+SIDL+EP+SO+LL+RF 0.19

6 Base slab bottom SW+SIDL+EPS+WP 0.13

The comparison between 2-D & 3-D FEM Model results has been done and it was found that there is little

variation in displacement presented in fig. 3 and fig. 4. The variation of displacement in line graphs

between 2-D FEM model and 3-D FEM model for top slab, bottom slab, left wall and right wall are shown

in fig.5, fig.6, fig.7 and fig. 8 respectively



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LOAD CASE 201

LOAD CASE 202

LOAD CASE 203

LOAD CASE 204

LOAD CASE 205

LOAD CASE 211

LOAD CASE 212

LOAD CASE 213

LOAD CASE 214

Fig.3. Displacement diagrams (2-D) (STAAD Pro V8i.)



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LOAD CASE 201

LOAD CASE 202

LOAD CASE 203

LOAD CASE 204

LOAD CASE 205

LOAD CASE 211

LOAD CASE 212

LOAD CASE 213

LOAD CASE 214

Fig.4. Displacement diagrams (3-D) (STAAD Pro V8i.)



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Fig.5. Displacement variation of bottom slab (STAAD Pro V8i.)

Table.4 Displacement variation of bottom slab (STAAD Pro V8i.)

Load

Case

Displacement

Y mm (2-D)

Displacement

Y mm (3-D)

201 -1.039 -0.985

202 -1.273 -1.206

203 -1.472 -1.305

204 -1.62 -1.445

205 -1.62 -1.445

211 -0.468 -0.539

212 -0.666 -0.638

213 -0.814 -0.778

214 -0.814 -0.778

-1.8

-1.6

-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215

DIS

PLA

CEM

ENT(

mm

)LOAD CASE

2D 3D



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Fig.6. Displacement variation of right wall (STAAD Pro V8i.)

Table. 5 Displacement variation of right wall (STAAD Pro V8i.)

Load

Case

Displacement

X mm (2-D)

Displacement

X mm (3-D)

201 -1.351 -1.431

202 -1.41 -1.49

203 0.688 0.734

204 0.634 0.678

205 6.244 6.63

211 -1.426 -1.785

212 0.673 0.44

213 0.619 0.384

214 6.229 6.336

-3

-2

-1

0

1

2

3

4

5

6

7

8

200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215

DIS

PLA

CEM

ENT(

mm

)LOAD CASE

2D 3D



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Fig.7. Displacement variation of top slab (STAAD Pro V8i.)

Table.6 Displacement variation of top slab (STAAD Pro V8i.)

Load

Case

Displacement

Y mm (2-D)

Displacement

Y mm (3-D)

201 0.993 1.18

202 0.897 1.098

203 -3.905 -3.836

204 -3.924 -3.843

205 -3.924 -3.843

211 1.988 2.218

212 -2.814 -2.715

213 -2.834 -2.723

214 -2.834 -2.723

-5

-4

-3

-2

-1

0

1

2

3

200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215

DIS

PLA

CEM

ENT(

mm

)LOAD CASE

2D 3D



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Fig. 8 .Displacement variation of left wall (STAAD Pro V8i.)

Table.7 Displacement variation of left wall (STAAD Pro V8i.)

Load

Case

Displacement

X mm (2-D)

Displacement

X mm (3-D)

201 1.351 1.431

202 1.41 1.49

203 -0.688 -0.734

204 -0.634 -0.678

205 4.976 5.274

211 1.854 1.785

212 -0.244 -0.44

213 -0.19 -0.384

214 5.42 5.568

-2

-1

0

1

2

3

4

5

6

200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215

DIS

PLA

CEM

ENT(

mm

)

LOAD CASE

2D 3D



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Fig.9 and Fig.10 shows the intensity of equivalent lateral raking force using 2D and 3D model respectively.

Intensity of raking force for 2D model calculated is 111.6 KN/m and for 3D model calculated is 121.5 KN/m

Fig.9. Equivalent lateral Racking Force corresponding to 2D model (STAAD Pro V8i.)

Fig.10. Equivalent lateral Racking Force corresponding to 3D model (STAAD Pro V8i.)

IV. CONCLUSIONS

For the design of cut & cover tunnel, 3-D finite element analysis was conducted. Finite element model

simulate the complete geometry of the tunnel. All possible loads were considered for the design as per IRC

Specifications. It can be concluded from the 2-D & 3-D analysis of tunnel that 2-D modelling may not be

sufficient to capture the actual behaviour of the structure and the critical 3D effects may be lost. There is

very little variation between 2-D & 3-D FEM Displacement & Moments results but 3-D FEM is more robust

in extracting forces from the stress contours. The intensity of raking force calculated using 2D model is

111.6 KN/m and using 3D model is 121.5 KN/m. This little difference is due to the fact that raking



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displacement is lower for 2D analysis than 3D analysis as the 2D structure is more rigid. From the results

presented in this paper, it was also observed that maximum compressive/tensile stresses are well within the

permissible stresses.

ACKNOWLEDGMENT

I would like to express my sincere thanks to faculty and support staff of Department of Civil Engineering,

College of Engineering Roorkee for providing the facilities to conduct the research on the topic.

REFERENCES

[1] Faraji. S, Qingping. Z, Far. M, & Kordestani. H, ―A Simplified Method for the Seismic Analysis of Urban Transportation Tunnels‖. International journal of

geology, vol. 8, pp. 1-4, 2014

[2] Hashash. Y, Hook. J, Schmidt. B, & Yao. J, ―Seismic Design and Analysis of Underground Structures, Tunnelling and Underground Space Technology‖,

vol. 16, pp. 247-293, 2001

[3] J. Jimenez, ―Free-Field racking deformation methodology applied to the design of shallow tunnel structures in high risk seismic areas. Practical

considerations‖. In: Tenth U.S National Conference on Earthquake Engineering, Frontiers of earthquake engineering, Alaska: Anchorage, pp: 21-25, 2014

[4] N. Newmark, ―Problems in wave propagation in soil and rock‖, Proceedings of the International Symposium on Wave Propagation and Dynamic Properties

of Earth Materials, 1968

[5] G.N. Owen & R.E Scholl, ―Earthquake engineering of large underground Structures‖, Report no. FHWA RD-80 195. Federal Highway Administration and

National Science Foundation, 1981

[6] Wang. J, "Seismic Design of Tunnels - A Simple State-of-the-Art Design Approach", William Barclay Parsons Fellowship, Parsons Brinckerhoff,

Monograph 7, 1993

[7] IS 456, Plain and Reinforced Concrete-Code of Practice (Fourth Revision), Bureau of Indian Standards, New Delhi, 2000.

[8] IS 1893, Criteria for Earthquake Resistant Design of Structures-Part 1, General Provisions and Buildings (fifth revision), Bureau of Indian Standards, New

Delhi, 2002.

[9] EN 1992-1-1, Euro code 2: Design of concrete structures - Part 1-1: General rules and rules for buildings [Authority: The European Union per Regulation

305/2011, Directive 98/34/EC, Directive 2004/18/EC], Europe,2004.

[10] IRC: SP: 84, Manual of Specifications & Standards for four laning of highways through public private partnership (first revision), Indian roads congress

2014.

[11] IRC: 6, Standard Specifications and Code of Practices for Road Bridges, Section-II, Loads and Stresses (Revised Edition), Indian Road Congress, 2014.

[12] IRC: 112, Code of Practice for Concrete Road Bridges, Indian Road Congress, 2014.

[13] IS 1786, High Strength Deformed Bars and Wires for Concrete Reinforcement. Specification (Fourth Revision), Bureau of Indian Standards, New Delhi,

2008.



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