Excavation Scheme for a Deep Wagon Tippler at Jawaharlal Nehru Port Trust, Bombay

CONTENTS

Certificate

Acknowledgement

Abstract

List of Figures

List OF Tables

LIst Of Photographs

List of Symbols

Chapter I GENERAL Introduction

Chapter II Alternative Schemes for Deep Excavation

2.1 Introduction
2.2 Open Excavation
2.3 Excavation after Soil Stabilization
2.4 Sheet Pile Wall
2.5 H–Beam Wall
2.6 Bored Pile Wall
2.7 Diaphragm Wall
2.8 Final Choice of Excavation Scheme

CHPATER III Site Visit at JNPT Mumbai

CHAPTER IV Analysis of Soil Data

4.1 Introduction
4.2 Soil Condition on site
4.3 Calculation of Earth Pressure
4.4 Calculation of Differential Water Pressure

CHAPTER V Analysis of Deep Wagon Tippler

5.1 Introduction
5.2 Calculation of Soil Springs
5.3 Calculation of Seismic Force
5.4 Calculation of Total Pressures per Panel
5.5 FEM-Analysis of the Structure (STAAD-III Package)
5.6 Analysis Results and Discussion

CHAPTER VI Summary

Appendices A & B

References

List of Figures

Figure 2.1: Alternative Schemes for Deep Excavation

Figure 2.2 H-Beam Wall Reference [17]

Figure 2.3 Schemes of Bored Pile Walls

Figure 2.4 Construction of Diaphragm Wall Reference [17]

Figure 2.5 Cantilevered, Strutted and Anchored Retaining Wall Reference [17]

Figure 4.1 Distribution of Water Pressure on the Structure

Figure 5.1 Calculation of Total Pressure per Panel

Figure A.1: Map of India – Earthquake Zones Reference [11]

Figure A.2: Zone Factor a0 for Calculation of Seismic Force Reference [11]

Figure A.3: Factor b for Calculation of Seismic Force Reference [11]

Figure A.4: Importance Factor I for Calculation of Seismic Force Reference [11]

Figure A.5: Relationship between SPT (N) and ES for Cohesive Soil Reference [20]

Figure A.6: Relationship between SPT (N) and ES for Sand Reference [20]

Figure A.7: Site Plan JNPT Mumbai Reference [16]

Figure A.8: Soil Profile JNPT Mumbai

Figure A.9: Distribution of Net Earth Pressure

Figure A.10: Distribution of Active Earth Pressure

Figure A.11: Elevation of a Deep Wagon Tippler

Figure A.12: Reinforcement Details of Diaphragm Wall with T-Section

Figure B.1: Comparison of Theoretical Passive Earth Pressure and Support Reactions

List of Tables

Table 5.1 Partial Safety Factors for Loads in Limit State Design Reference [12]

Table A.1 Soil Data JNPT Mumbai

Table A.2 Calculation of Active Earth Pressure

Table A.3 Calculation of Passive Earth Pressure

Table A.4 Total Earth Pressure per Panel

Table A.5 Total Differential Water Pressure per Panel

Table A.6 Total Pressure per Panel

List of Photographs

Photo 2.1 Excavation Scheme with Strutted Steel Sheet Pile Walls Reference [22]

Photo 3.1 Construction of Diaphragm Wall at JNPT Mumbai, India

Photo 3.2 Construction of Diaphragm Wall – Excavating with Bailer

Photo 3.3 Construction of Diaphragm Wall – Guide Wall

Photo 3.4 Construction of Diaphragm Wall – Manufacturing of Reinforcement Cage

Photo 3.5 Construction of Diaphragm Wall – Filling with Concrete

List of SYMBOLS

a Angle of inclination of a slop to horizontal [°]

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Certificate

This is to certify that the project entitled “Excavation Scheme for a Deep Wagon Tippler at JNPT Mumbai” submitted by Mr. Thoralf Schlüter, is a bonafide record of work carried out by him under our supervision. This work has been carried out under the DAAD – ISP Program between Technische Universität Hamburg – Harburg and Indian Institute of Technology Madras.

Acknowledgement

I wish to thank Dr. S.R. Gandhi, Associate Professor & Head of the Geotechnical Engineering Division, Department of Civil Engineering, IIT Madras, for his guidance and constant encouragement during the course of my project work.

I also wish to thank Dr. R. Sundaravadivelu, Associate Professor, Ocean Engineering Center, IIT Madras, for his guidance, his encouragement during my stay at the IIT Madras and for making my site visit at JNPT Mumbai possible.

I wish to thank Dr.-Ing. J. Grabe, Professor and Head of the Arbeitsbereich Geotechnik und Baubetrieb, Technische Universität Hamburg – Harburg, for his encouragement.

Further I wish to thank Dr.-Ing. M. Luber, Oberingenieur of the Arbeitsbereich Geotechnik und Baubetrieb, Technische Universität Hamburg – Harburg, for his encouragement and for providing me with documents used in this project.

Finally I wish to thank Dr.-Ing., Dr.-Ing. E. h. mult. O. Mahrenholtz, Arbeitsbereich Meerestechnik II, Technische Universität Hamburg – Harburg, for making my stay in India possible.

Thoralf Schlüter

ABSTRACT

The JNPT near Bombay is having most of the area covered by a thick soft clay deposit at surface. Development of port requires underground structures like wagon tippler to unload bulk cargo like coal, iron ore, etc. The depth of the structure below ground level is about 12 m. In view of the high ground water table and poor shear strength of the strata, construction of such structure requires careful planning and execution.

This project work will include the following aspects:

1. Alternative schemes for deep excavation like open excavation, excavation with sheet pile, excavation with bored pile wall and use of RCC diaphragm wall. The final choice of excavation shall be arrived based on relative merits and demerits of above schemes.
2. Detailed analysis of soil data to arrive at earth pressure on the wall.
3. Detailed stability analysis of the structure under the external forces like earth pressure and earthquake force.

For detailed analysis of the structure the software package STAAD III based on the Finite Element Method will has been used.

CHAPTER I GENERAL INTRODUCTION

The Jawaharlal Nehru Port Trust, called JNPT, is situated close to Mumbai (former name Bombay) at the same channel used by Mumbai Port and Jawahar Dweep Oil Terminal. It is the youngest and most modern port of India. Commissioned in May 1989, the port still has high development ambitions especially in the sector of expansion, which is necessary in view of its purpose of decongesting Mumbai Port and the serving as a Hub Port for this region. The new Nhava Sheva Container Terminal Project is an example for the continuous progress in realising these plans.

In carrying out of these plans, structures like deep wagon tippler are required for managing bulk cargoes at the bulk terminals. This type of structure allows an economical unloading of cargoes from trains. Because of the necessary depth of a wagon tippler the cargoes have to surmount a difference in altitude of about 12 m from ground level and additional the difference in altitude from ground level up to the vessel. This can only be done by using long conveyor tunnels. An elevation of the cross section for a typical deep wagon tippler, borrowed from an existing structure.

In the first part of this project work, a review on different, often used schemes, for deep excavations is done to find out a favourable excavation scheme for construction of a deep wagon tippler. The choice for a structure using RCC diaphragm walls as retaining walls is based on its merits under the existing soil conditions and on a possible serving as part of the final structure. During a site visit to JNPT the decision for this type of excavation scheme was discussed with site engineers, who have experience in constructing RCC diaphragm walls under existing soil and groundwater conditions.

Finally an analysis of a typical cross section of the deep wagon tippler has been carried out by using the structural engineering software STAAD III, based on the Finite Element Method. The safety of the structure against failure caused on external and internal loads is proofed as well as for the case of an earthquake, which will be very possible, because of the location of the site in the earthquake zone four.

CHAPTER II ALTERNATIVE SCHEMES FOR DEEP EXCAVATION

2.1 Introduction

A deep excavation has to be secured against failure based on external forces like active earth pressure, water pressure and exceptional loads like earthquake force. Using different construction schemes to take the acting loads can ensure this. While at open excavations the static safety is given by constructing a sufficient slope. In case of retaining walls the acting loads are taken by anchors, struts and/or by the passive earth pressure. To stabilise the soil on the site and to reduce the acting forces consequently, a ground improvement method can be used before starting with the construction of an excavation. A subdivision of possible and often used schemes is shown in the following figure:

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2.2 Open Excavation

An open excavation is used when the construction site has enough space for excavating the soil and if the soil has sufficient shear strength. High ground water tables constitute difficulties in construction of open excavations.

The sides of the excavation are unsupported and the safety device against failure based on earth pressure is given by constructing a sufficient slope. In case of high differences between ground and dredge level the construction of berms is required to safe the slope against slipping or to make dewatering possible.

Because of the poor shear strength of the soil and the high ground water table on site an open excavation is not favourable for a type of construction like deep wagon tippler at the JNPT Mumbai. The dredge level at 12 m below ground level requires a very large area for the excavation. The limited working space of construction equipment like excavators indicates the arising of difficulties while constructing the final structure. A necessary dewatering of the excavation would be very difficult.

2.3 Open Excavation after Soil Stabilisation

The open excavation can also be constructed after carrying out a ground improvement. This method will be used to increase the stiffness and strength of the soil or to reduce its permeability for water. Because of this the acting loads based on earth and water pressure and the required area for the excavation will be reduced. A ground water control will be much easier.

Different methods for ground improvement can be distributed:

- Soil replacing
- Deep compaction (dynamic compaction, Vibro flotation soil compaction,)
- Consolidation grouting
- Consolidation by preloading
- Vertical drainage system (vertical band drains,)
- Grouting (soil fracturing, compaction grouting, jet grouting)
- Compaction by using proctor compaction curve

Depending on the soil and the type of structure these methods can also be used to improve the soil before constructing a retaining wall.

2.4 Sheet Pile Wall

Sheet pile walls are made of steel sections, timber or reinforced concrete with large moments of inertia. The steel sheet pile wall is the most common and widely used type. The connection of the individual piles is given by so called locks. Side by side a series of sheet piles will be driven or vibrated into the ground and supported by anchors or struts. They act on the sheet piles through walings. As a result of the small cross section of steel sheet piles, they can easier be driven into the soil with smaller shocking than other types of sheet piles. Because of that they can be brought into action close to other buildings. The pulling of the sheet piles can mostly be done without any settlement of the soil. Generally steel sheet piles are waterproofed

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Sheet piles are often brought into action for excavations in areas with high ground water table and for constructions into open water. An important feature of this excavation scheme is the withdrawing and re-use of the steel sheet piles. Further advantages are such as being lightweight, possessing resistance to high driving stresses and a possible serving as parts of structures and their foundations. The sheet pile wall is one of the oldest and widely used types of retaining walls. However, in India steel sheet pile walls are more expensive than cast-in-place walls because of the necessary import with high duties.

2.5 H-Beam Wall

This type of excavation scheme is also called s oldier pile wall or Berlin Wall, because of its first use during the construction of the Berlin underground.

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The support of the soil is given by a combination of planks made of timber in a horizontal lagging and vertical steel soldier piles.

The vertical piles will be driven or vibrated into the ground before excavating the soil. In case of very stiff soil strata or if a quiet construction is required, the piles can be set into bored holes. After this the remained space can be filled with sand or other materials. The soldier piles should be founded at least 1.5 m below the dredge level of the excavation, if the level of support by anchors or struts is not deep enough. During construction the placing of the planks should be maximally 1m above the level of the excavated soil. The individual soldier piles and the anchors or struts respectively are connected by horizontal walings.

This excavation scheme can take higher bending moments than sheet pile walls. Because of the possible adaptation of the spacing between the soldier piles, H-Beam Walls are very flexible in case of local difficulties, like crossing supply lines. This method for deep excavation is very economical and often used, especially in inner-city locations.

2.6 Bored Pile Wall

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Bored pile walls are made of lined up bored piles. Three types of walls can be distributed, shown in figure 2.3.

While constructing the spaced bored pile wall the space between the piles will be infilled with shotcrete or cast-in-place concrete. Contiguous pile walls have spacing between the piles of 2-5 cm depending on the type of soil. The piles of spaced and contiguous bored pile walls are made of reinforced concrete. Both types of pile walls provide an economical option where ground water problems are not anticipated. Secant pile walls can be constructed in almost all kinds of soil and are suitable in cases where the retaining wall must be waterproof. At the secant pile wall the dimensions of the overlapping is given by 10 to 20 % of the pile diameter. The primary piles only have an infilling effect. Because of this they will be constructed with concrete of less quality. The secondary piles will be constructed only a few days later as long as the concrete of the primary piles is not dry yet. Steel reinforcement is used to give higher stiffness to these piles.

Bored pile walls will be constructed up to a depth of 25 m below ground level. They have a very insignificant deformation and a precision in vertical direction up to 0.05%. The construction of the piles is considerate because of the casing method. The costs for bored pile walls are higher than for either H-beam walls or sheet pile walls and about equal to the use of diaphragm walls.

2.7 Diaphragm Wall

The construction of diaphragm walls takes place in the subsoil and will be done in different sections. Excavator or fraise/cutter can excavate the trenches. While fraises or cutter have a very high performance and a high precision in the view of the verticality, excavators are very economic for small wall areas up to 5000 m2. The individual sections will be excavated, reinforced and filled with concrete one after another. A tube set into the trench serves as formwork. It will be pulled while concreting.

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Generally three types of construction methods can be distinguished. In the first method, shown in figure 2.4, a not drying Betonite suspension is given into the trench to support against earth pressure while excavating.

After reaching the final depth and setting the reinforcement cage, the trench will be filled with concrete by using the Tremie Method. The Betonite will be displaced upwards by the concrete and can be treated and re-used. The second method is mostly used for impervious walls. The supporting suspension based on cement is drying slowly and will not be replaced. Setting pre-cast concrete panels or steel sheet piles into the trench can complete this method. After final excavation, diaphragm walls can serve as retaining walls and beyond this they can serve as deep foundations to give loads into deeper strata. They can also act as impervious diaphragm walls.

In comparison to bored pile walls, diaphragm walls have about the same deformation values. In advantage to bored pile walls they can be reinforced in a larger width. Today diaphragm walls can be constructed up to a depth of 150 m. The allowable width of the panels is depending on the type of soil, depth of the trench, ground water table and unit weight of the supporting suspension. Normally widths between 2.5 and 5 m are used, seldom widths between 1.2 and 8 m. The usually thickness of a wall is between 0.4 m to 3 m.

In contrast to pile walls the construction of diaphragm walls requires extensive equipment at the construction site, especially in the view of the necessary installation for Betonite recycling. In the view of this difference the use of bored pile walls for smaller projects with a smaller depth is more economical.

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Retaining walls for deep excavations are usually tied back by grout anchors regardless of the type of soil or supported by temporary struts. The three different types of retaining walls are shown in figure 2.5.

In difference to cantilevered retaining walls where the only source of stability is the penetration into the soil, anchored walls have the additional support by anchoring. The anchors are often used for permanent support of a structure. This method has been a widely accepted geotechnical method for many years.

However, it is not used for the construction of the deep wagon tippler at JNPT in this project. The poor soil conditions of the soft clay strata would require an anchoring into the deep strata of basalt rock.

In case of strutted walls the additional support is given by bracing the excavation with struts. They are brought into action when a temporary support of the walls is required. In view of the reduced space for the excavators an excavating of soil is difficult.

2.8 Final Choice of Excavation Scheme

For construction of a deep wagon tippler an excavation of soil up to the depth of 12 m below ground level is required. Arising high earth pressure based on this depth and the poor shear strength of the soil at the site, a high ground water table and the high probability of additional loads based on earthquakes make high demands on the excavation scheme.

An excavation scheme with RCC diaphragm walls is chosen.

This type of structure is very resistant to high bending moments because of its continuous reinforcement along the wall. An additional support by using a T-shape for the cross section of the wall is possible. This would not be possible in case of bored pile walls.

In the view of the type of structure, which has to be constructed, especially the possible serving as a foundation of the final structure will make the diaphragm walls an economical construction scheme. In this way a replacing of the excavation scheme after constructing the final structure is not necessary.

The already existing equipment at the construction site at JNPT, required for construction of diaphragm walls, and the concentrated experience in using this type of structure under the existing soil conditions, are other reasons for choosing this excavation scheme for the construction of a deep wagon tippler.

CHAPTER III Site Visit at JNPT Mumbai

To get an insight into the construction procedure at Indian construction sites, I visited a construction site at the JNPT Mumbai with two faculties from the Ocean Engineering Center of IIT Madras from March 7th to March 3rd, 2000.

The visited site belongs to the project “Construction of Shallow Water Berth and Extension of Port Craft Berth for handling general container cargo at JNPT Mumbai” and is one of the most modern construction sites in India. The visit included the study of the construction of RCC diaphragm wall and RCC Pile Foundations. The construction of an RCC diaphragm wall is documented in the photographs below.

The excavation of the trench was done by excavator and bailer (photo 3.2). A Betonite suspension was used to stabilise the sides of the trench against earth pressure. The filling with concrete was done by using the Tremie Method (figure 2.4) and is documented in photo 3.5. I could also visit the place for manufacturing of reinforcing cages. This procedure is shown in Photo 3.4. Additional I visited the laboratory at the site, which is responsible for checking the producing and the quality of the used concrete. A check of the grading curve of the concrete aggregate and the proof of the compressive strength of five concrete test specimens has been done. I could also see the manufacturing of concrete, which has taken place at to the construction site. There I could attend a measure of the slump of the concrete.

In the following pages some photographs show the construction of the diaphragm wall.

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CHAPTER IV ANALYSIS OF SOIL DATA

4.1 Introduction

The founding of a structure requires a thorough soil investigation to get the existing soil conditions. With results of these investigations the engineer is able to arrive earth and water pressure as loads on the structure. Its static stability can be proofed. In this Chapter the analysis of the soil data for the construction site at JNPT is carried out.

4.2 Soil Condition at Site

A thick soft clay deposit at the surface covers most of the area of the new JNPT. Strata of soft clay are typical for construction sites at ports or at areas situated close to the coastline. Low shear strength and a high ground water table make this soil a difficult underground for founding a structure.

For the construction of port and harbour structures at the site a ground improvement was carried out. For that purpose the former ground level of -0.7 m was filled up to +7.1 m after settlement of the fill. The used material is a murrum fill made of light brown sandy gravel with boulders. After the final settlement the fill has a thickness of 9.1m up to a level of -2.0 m The layer has an angle of internal friction j = 40° and up to the depth of the ground water table a saturated unit weight of gsat = 20 kN/m3.

The unit weight of the soil strata below the ground water table is assumed as gsub = 10 kN/m3, equal to the unit weight of water. Up to depth of -8.5 m the murrum fill is followed by different strata of marine silty clay with increasing cohesion values from 28 to 100 kN/m2 in average. The increasing (SPT) N values, found out by the standard penetration test are used to work out the modulus of compressibility of the soil ES. These strata have an angle of internal friction of 0°. Below the depth of -8.50 m the soil has a thick stratum of basalt rock with a cohesion value of 700 kN/m2 and (SPT) N value of 100.

The tide level for JNPT Mumbai are given as:

- Highest High Water Level (HHWL) + 5.38 m
- Mean High Water Spring (MHWS) + 4.42 m
- MEAN HIGH WATER NEAPS (MHWN) + 3.30 m
- HIGHEST LOW WATER (HLW) + 2.74 m
- MEAN SEA LEVEL (MSL) + 2.51 m
- MEAN LOW WATER NEAPS (MLWS) + 1.85 m
- MEAN LOW WATER SPRINGS (MLWS) + 0.76 m
- LOWEST LOW WATER (LLW) – 0.44 m

A soil profile of the soil condition at the site is given in figure A.8. Values for the different strata are given in table A.1.

During excavation of site fill, it is noticed that large quantity of soft clay has got displaced towards the sea. This has reduced the actual thickness of the soft clay shown in soil profile (figure A.8). However, on conservative side, the design is made as per the soil profile.

4.3 Calculation of Earth Pressure

The analysis of the structure requires the calculation of the earth pressure acting on the diaphragm walls. The lateral active and passive earth pressures are given as:

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[4.1]

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[4.2]

Where:

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The coefficients of active and passive earth pressure are calculated by using the equations 4.3 and 4.4, worked out by Mueller-Breslau:

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[4.3]

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[4.4]

Where:

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The calculation was done manual by using the above mentioned formulas. Results of active and passive earth pressures up to a depth of -18.5 m are given in the tables A.2 and A.3. A chart for the net earth pressure and a distribution of on the wall acting earth pressure is given in figure A.9 and figure A.10 respectively. The point of zero net pressure is found out at the depth of –5.50 m. In the stability analysis of the structure the earth pressure has to be used for the calculation of acting loads up to this depth. Below this the passive pressure gives a support to the diaphragm wall. In the analysis the support is idealised by elastic soil springs.

From –8.5 m on the stratum of basalt rock leads to very large values of passive earth pressure. This indicates a good condition for founding the diaphragm wall into this layer especially in the view of a possible settlement of the structure and the hydrostatic uplift forces acting on it. For the analysis of the diaphragm wall the earth pressure will be calculated as total pressures per panel. Details of this calculation are given in 5.3.

4.4 Calculation of Differential Water Pressure

The soil at the construction site has the ground water table at a depth of +1.60 m. Because of the different water tables on the final structure the water pressure, acting on the diaphragm walls, is calculated as differential water pressure. The situation at the site while using a construction scheme with diaphragm walls and the distribution of water pressures on it is shown in the figure 4.1. The differential water pressure is given as:

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[4.5]

Where:

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Here the difference between the water tables on the ground water and on the dredge level is given as h = 6.50 m. The differential water pressure can be calculated as 65,0 kN/m2.

It is acting on the diaphragm wall up to the dredge level and will be calculated as the total differential water pressure per panel for the analysis.

Further it is required to check the safety of the structure in the view of hydrostatic uplift. The acting uplift force is equal to the differential water pressure. It is given as:

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[4.6]

Where:

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CHAPTER V ANALYSIS OF DEEP WAGON TIPPLER

5.1 Introduction

The basic aim of analysing retaining walls is to proof the stability of the excavation sides. Further the analysis serves for the designing of the walls and other supporting structural members. The stability under hydrostatic uplift force and a possible settlement of the structure has to be proofed. For calculation a complicated problem of the structure-soil interaction is given. Active and passive earth pressures are only borderline cases, appearing when a sufficient moving of the wall is given. States between these cases are difficult to count. Complicated design codes are given all over the world. For this project, calculation methods based on the concepts of active and passive earth pressure are used.

The construction of a deep wagon tippler at JNPT Mumbai requires an excavation of the soil up to 12 m below ground level. To enable this it is necessary to support the excavation sides during the construction phase. A structure consisting of two cantilevered diaphragm walls, supported by fixation in the soil and connected by a 0.5m thick deck slab at dredge level, has to be proofed for its static stability.

5.2 Calculation of Soil Springs

The soil support below the dredge level is represented by elastic springs. The calculation of stiffness of the soil springs is done in the following manner.

The SPT (N) values of the soil make it possible to find out the modulus of compressibility ES for the strata by using the relationship N vs. ES for cohesive soils, given by Mori (1965) and reproduced in figure A.5. Individual values for the different strata are given in table A.1.

Further the modulus of subgrade reaction KS will be used for calculating the spring constants. This value is worked out using Vesic’s Theory (1972), shown in formula 5.1. Results are given in appendix B.

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[5.1]

Where:

KS = modulus of subgrade reaction [kN/m3]

B = panel width of the beam [m]

ES = Young's modulus of soil [kN/m2]

Eb = Young's modulus of beam [kN/m2]

Ib = moment of inertia of the beam section [m4]

mS = poison's ratio of soil

The value of 0.65 is used for the rectangular section of the beam. For circular sections being found at pile structures a value of 1.3 has to be used.

The panel width of the diaphragm wall is chosen as B = 2.50 m. The Young's modulus of the beam Eb is given by formula 5.2:

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[5.2]

Where:

Eb = Young's modulus of beam [kN/m2]

fck = shear strength of concrete

(M40 with shear strength of 40 N/mm2 is used as material of the beam)

Using this value the modulus of the beam can be calculated as:

Eb = 5700 * Ö(40 N/mm2) = 3.605*107 kN/m2

Finally the soil spring stiffness is worked out by using Newmark’s Equation (1942).

For the top spring:

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[5.3]

For intermediate springs:

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[5.4]

For bottom spring:

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[5.5]

Where:

K1, KI, Kn = stiffness of soil springs [kN/m]

B = panel width of beam [m]

L = thickness of wall = length of element [m]

KS = modulus of subgrade reaction at depth of the spring

The Calculation of KS values of the soil and soil spring constants are done by using MS Excel. The spacing between springs is worked out as 0.85 m by using Prescription 5.6:

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[5.6]

Where:

S = spacing between nodes [m]

L = thickness of the diaphragm wall [m]

All results of these calculations are given separate for each analysis in appendix B.

5.3 Calculation of Seismic Force

In view of the high earthquake risk in the area of the construction, the planing of the structure requires the consideration of forces caused by this natural phenomenon.

To consider external loads based on earthquakes, horizontal point loads acting on the top nodes of both diaphragm walls are used. Both forces have the same direction. For the calculation of horizontal force caused by earthquakes, the seismic coefficient method given in the Indian Standard Code IS: 1893 (1984), is used. The following equations are given for the calculation.

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[5.7]

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[5.8]

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[5.9]

Where:

FH = horizontal seismic force [kN]

aH = design horizontal seismic coefficient

Wm = weight of mass under consideration ignoring reduction due to buoyancy of uplift

bs = coefficient depending on the soil foundation system Þ b = 1.0 refer to figure A.3

I = coefficient depending on importance of the structure Þ I = 1.0 refer to figure A.4

a0 = basic horizontal seismic coefficient based on the zone of earthquake risk

JNPT Mumbai is located at zone IV Þ a0 = 0.05 refer to figure A.2

DL = dead load of the structure [kN]

LL = live load acting on the structure [kN]

The live load is assumed as 10 kN/m2 on each side of the structure.

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The dead load depends on the dimension of the structure. It is calculated for each step of the analysis. Results are shown in appendix B. The density of material of the structure is assumed as 25 kN/m3 for steel reinforced concrete.

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Where:

DL = Dead Load [kN]

Vstructure = volume of the structure [m3

[...]