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A Study on Ground Deformation and Structural Response in Existing Tunnels Induced by Diagonally Aligned Adjacent Tunnel Excavation

  • 백문경 (아주대학교 일반대학원)

초록/요약

ABSTRACT As urbanization accelerates and surface-level land in metropolitan areas becomes increasingly saturated, the strategic development of underground space has emerged as a critical solution for expanding urban infrastructure. In particular, the growing need to excavate new tunnels in close proximity to existing ones poses complex challenges, including stress redistribution, ground deformation, and potential structural instability. Among these, diagonally aligned twin tunnels present particularly intricate soil–structure interaction behavior due to their asymmetrical configuration, requiring further investigation. This study proposes an integrated research framework combining physical model testing, high-resolution deformation analysis using Particle Image Velocimetry (PIV), and numerical simulation based on the Discrete Element Method (DEM) using PFC2D. Physical model tests using carbon rods were conducted to simulate granular soil behavior under six tunnel spacing scenarios, replicating excavation conditions with a scaled Tunnel Boring Machine (TBM) model. Ground deformation patterns and segmental load changes were measured and analyzed. The PFC2D simulations were calibrated against experimental data and extended to field-scale conditions, incorporating rock-like material properties to evaluate deformation and stress redistribution at real-world scale. The results demonstrate that the spatial configuration between tunnels significantly affects both ground behavior and localized structural responses. When the existing tunnel was located within the relaxation zone induced by the new excavation, well-formed arching effects failed to develop, leading to substantial segmental load reductions of up to 70% at the invert segments. In contrast, when the existing tunnel was positioned outside the influence zone, stress redistribution occurred more uniformly, and load variations remained within ±10%, indicating stable conditions. A segmental load ratio-based classification system was proposed to quantify the impact severity of adjacent excavation. The validated experimental-numerical framework provides a reliable basis for predicting structural responses and offers practical design guidance for determining minimum tunnel spacing, reinforcement needs, and risk mitigation strategies in dense urban environments. This research contributes to the development of a robust analytical tool for the planning, design, and construction of underground infrastructure, offering new insights into ground loosening and load transfer mechanisms in multi-tunnel settings and supporting safer, more sustainable urban subsurface development.

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목차

I. INTRODUCTION 1
1.1 Background and necessity 1
1.2 Objectives of the study 6
1.3 Scope and methodology 8
II. THEORETICAL BACKGROUND AND LITERATURE REIVIEW 11
2.1 Case studies on urban underground development and structural impact 11
2.2 Ground behavior mechanisms induced by excavation 18
2.3 Overview of numerical methods 24
2.3.1 Discrete Element Method (DEM) 25
2.3.2 Applicability analysis of DEM 26
2.3.3 Application of numerical analysis in urban geotechnical engineering 28
2.3.4 Criteria for selecting numerical analysis methods and integrated approaches 29
2.4 Summary of previous studies and research gap. 30
III. EXPERIMENTAL DESIGN AND PHYSICAL MODELING 33
3.1 Model ground and structure setup 34
3.1.1 Model ground 34
3.1.2 Configuration of the TBM tunnel structure model 37
3.1.3 Implementation of structure–ground interaction in model configuration 40
3.2 Measurement system and testing procedures 41
3.2.1 Configuration of Geo-PIV system and load measurement equipment 41
3.2.2 Initial calibration procedure and excavation simulation 43
3.3 Experimental variables 44
IV. NUMERICAL ANALYSIS AND MODEL VALIDATION 49
4.1 Overview of numerical approach 49
4.2 Modeling procedure and input parameters 50
4.2.1 Model geometry definition and boundary condition setup 51
4.2.2 Input of material properties and definition of mechanical parameters 51
4.2.3 Definition of contact model and initial stress state configuration 54
4.3 Validation and model calibration 56
4.3.1 Comparison of experimental and numerical results 56
4.3.2 Micro-parameter adjustment and error analysis 57
V. RESULTS 59
5.1 Overview 59
5.2 Model test results 61
5.2.1 Ground displacement measurement: PIV analysis 61
5.2.2 Load variations in the existing tunnel 67
5.3 Numerical analysis results and comparison: Model test case 72
5.3.1 Numerical analysis results of ground deformation due to tunnel excavation: Model test case 73
5.3.2 Numerical analysis results of load variations in existing tunnel: Model test case 76
VI. DISCUSSION 81
6.1 Comparison of load applied 81
6.2 Numerical analysis and comparison: Field scale 86
6.2.1 Material property correction considering rock mass characteristics 87
6.2.2 Interpretation model configuration and excavation conditions 88
6.2.3 Comparison of ground deformation in rock mass 89
6.2.4 Numerical analysis results of Load variations in the existing tunnel: Field scale 92
6.2.5 Interpretation and implications of analysis results 96
6.3 Critical considerations for adjacent tunneling 97
6.3.1 Increases/decreases ratio of earth pressure to existing tunnel segment 97
6.3.2 Effect of tunnel location on ground deformation and arching 103
6.3.3 Segmental Load Changes and Stress Redistribution 104
6.3.4 Implications and implications for tunnel design and risk assessment 105
VII. CONCLUSION 108
7.1 Conclusion 108
7.2 Recommendation for future studies 111
REFERENCES 113

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