桩荷载对粘土隧道结构影响的数值分析

摘要

通过对相关文献的调查研究，可以发现目前桩荷载对既有隧道的影响没有得到足够的重视。为保证隧道结构的安全可靠，研究不同土体中桩荷载对既有隧道结构力学响应的影响规律就显得十分重要。因此，本文采用有限元分析软件Plaxis，选取红土和上海、博姆、曼谷的典型粘土地层，分析了不同地层临近既有桩基对隧道结构力学响应的影响规律，进一步阐述了桩和隧道之间的相互作用机理。
　　首先，本文对比分析了红土与其它粘土地层中隧道的弯矩、轴力、剪力及变形，揭示了红土地层对隧道结构的特殊影响。结果表明，与其它地层相比，红土地层中隧道弯矩和剪力明显较大，轴力则无明显区别，隧道变形有大有小。
　　其次，本文研究了用于隧道衬砌上的桩承载效应的二维平面应变模型，以确定二维平面应变模型是否能较为接近的模拟三维模型的力学状态，并且分析何种情况下三维模型能够简化为二维平面应变模型。结果表明二维模型高估了桩的荷载效应，尤其在衬砌的位移方面。因此，二维模型应谨慎使用，且其结果只能作为一个大概值。
　　此外，本文还研究了桩荷载在不同地层中对隧道力学响应的影响，主要分析因素为土体刚度、静止土压力系数和桩与承台连接情况。结果表明:桩荷载效应较大程度上取决于土体刚度和静止土压力系数，桩与承台连接对桩荷载引起的隧道响应没有明显影响。相对土体刚度而言，静止土压力系数对桩荷载引起的隧道弯矩影响更大，对隧道变形和轴力的影响则较弱。而且桩的长度对衬砌变形和内力均具有重要的影响。与硬质粘土相比，软质粘土中的隧道会出现较高的弯矩、位移和较低的轴力。与曼谷粘土相比，红土地层中临近桩基的隧道的弯矩和变形更大。在曼谷硬粘土中，桩荷载对隧道弯矩和变形影响较小，但对其轴力影响较大。

目录

声明

ACKNOWLEDGEMENTS

摘要

ABSTARCT

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF SYMBOLS

1 INTRODUCTION

1．1 Problem Statement

1．2 Scope

1．3 Thesis Outline and Workflow

2 LITERATURE REVIEW

2．1 Pile Tunnel Interaction Problem

2．2 Lateritic Soils

2．2．1 Mineral Composition，Physical and Mechanical Characteristic of Lateritic Soils

2．2．2 Engineering Characteristics of Lateritic Soils

2．2．3 Constitutive Models and Features for Lateritic Soils

2．2．4 The Mohr-Coulomb’s Model

2．2．5 The Hardening Soil Model

2．2．6 Response Characteristics of Lateritic Soils to Tunnelling

2．3 Shanghai soft clay，Bangkok soft and stiff clays，Boom clay and London clay

2．4 Modelling Approach of Tunnel Problems

2．4．1 Modelling of Pile Group Effect on Tunnels

2．4．2 Embedded Piles in Plaxis 3D

2．4．3 Embedded Pile Row Element in Plaxis 2D

2．4．4 Induced Structural Forces in Tunnel Lining due to Pile Loads

3 3D COMPARATIVE ANALYSES OF FORCES AND DISPLACEMENTS OF TUNNEL LININGS IN CLAYS

3．1 Selection of Appropriate Soil Constitutive Models

3．2 Comparing Lining Force for Tunnels in Lateritic soilcomparingLining ateritic soil，Shanghai soft clay，Bangkok soft clay，Bangkok stiff clay，Boom clay and London clay

3．3 Modelling Approach

3．4 3D Model for Step-by-Step Validation

3．5 Parametric Analyses

3．6．1 Ground Surface Settlements

3．6．2 Lining Forces and Displacements

3．6．3 Influence of Soil Parameter on the Mechanical Response of the Tunnel Lining in Lateritic Soils

4 COMPARING THE EFFECTS OF PILE GROUP LOADS ON TUNNEL LINING USING 2D AND 3D MODELS

4．1 Finite Element Analyses

4．1．1 Determining Load Capacity of Pile

4．1．2 Finite Element Model for 2D Plain Strain Analyses

4．1．3 Validity of the 2D Plain Strain Model

4．1．4 Finite Element Model for 3D Analyses

4．1．5 Constitutive Model and Material Properties for 2D Model

4．1．6 Constitutive Model and Material Properties for 3D Model

4．1．7 Numerical Simulation of the Pile-Tunnel Interaction

4．2 Results

5 EFFECTS OF PILE GROUP LOADS ON TUNNELLINING IN SOFT AND STIFF CLAYS USING A 3D MODEL

5．1 Model Geometry and Boundary Conditions

5．2 Materiai Parameters and Constitutive Models

5．3 Determination of Allowable Design Load of the Piles within the Various Clays

5．4 Numerical Analyses Procedure for the Studies

5．5 Model Validation

5．6 Results

5．6．1 Comparing Pile Loads Effects on Tunnel Lining in Lateritic Soil，Bangkok Stiff Clay and Bangkok Soft Clay

5．6．2 Accessing the Influence of Soil Stiffness Modulus(E50ref)and At-Rest Earth Pressure Coefficient(Ko)on Pile Group Load Effects on Tunnel Lining

5．6．3 Influence of Pile Head Connection on Pile Group Load Effects on Tunnel Lining

5．6．4 Influence of Pile length on the Pile Group Load Effects on Tunnel Lining

6 CONCLUSIONS

REFERENCES

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