Numerical Analysis of the Effect of Pre-stress on Excavation Supports｜國立臺灣科技大學博碩士論文系統

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研究生：	柯敏柔 Mara St. Clair
論文名稱：	Numerical Analysis of the Effect of Pre-stress on Excavation Supports Numerical Analysis of the Effect of Pre-stress on Excavation Supports
指導教授：	歐章煜 Chang-Yu Ou
口試委員:	廖瑞堂 Ray-Tang Liao 熊彬成 Benson Hsiung 謝百鉤 Pio-Go Hsieh
學位類別：	碩士 Master
系所名稱：	工程學院 - 營建工程系 Department of Civil and Construction Engineering
論文出版年：	2017
畢業學年度：	105
語文別：	英文
論文頁數：	241
中文關鍵詞：	pre-stress 、tieback 、braced 、deep excavation 、numerical analysis
外文關鍵詞：	pre-stress, tieback, braced, deep excavation, numerical analysis
相關次數：	點閱：233 下載：7
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The purpose of this study is to analyse the impact of pre-stress on a tieback excavation system. Previously, Peck et al. (1974) showed that the pre-stressing of struts and tiebacks considerably decreases ground movements thus concurrently reduce settlements adjacent to an excavation but these notes did not include the effects on the supports in an excavation system. The well-established effective stress Hardening Soil model in tandem with the popular finite element analysis software, PLAXIS 2D is employed to simulate the soil-structure interaction and behaviour for the National Taiwan University Hospital basement excavation under plane strain conditions. The calculated input parameters for the initial 2D model are used in a parametric study to analyse variations in the soil-tieback fixed section mobilised shear strength distributions, tieback fixed section length and Mohr-Coulomb plastic points with pre-stress. The mobilised shear strength distribution is used to estimate suitable fixed section lengths of tiebacks installed in the silty sands of Taipei, Taiwan. From the mobilised shear strength distributions for anchor diameters of 0.114m, a fixed length of 16.0m to 20.0m installed at a pre-stress load equal to 100 - 120% of the design load is suggested as an appropriate length since, a factor of safety attained from a c/phi reduction analysis surpassed the required minimum factor of safety of 1.6 for temporary tieback systems. A braced excavation case, the Cathay Life Insurance Office Building also constructed in Taipei, Taiwan, is modelled to compare the observed differences in the effect of pre-stress in both support systems. Pre-stress is found to have little effect on maintaining the stability of a braced excavation but seems to control the stability of a tieback excavation system.

Abstract III
Acknowledgements IV
List of Tables VIII
List of Figures IX
Chapter 1 1
Introduction 1
1. Background 1
2. Objectives 1
3. Thesis Structure 2
Chapter 2 3
Literature Review 3
1. Introduction to Tieback Excavation Systems 3
1.1. Types of Ground Anchors 5
1.2. Tieback Free Section 6
1.3. Tieback Fixed Section 6
1.4. Tieback Loads 9
1.5. Pre-stressing Anchors 10
2. Elastoplastic Constitutive Soil Models 12
2.1. Overview of the Hardening Soil Constitutive Model 12
2.2. Hardening Soil Model Parameters 13
2.3. Drained Analysis 14
2.4. Undrained A Analysis 14
3. Finite Element Models of Tieback Excavations in PLAXIS 2D (2015) 14
3.1. Node-to-node Anchor 15
3.2. Embedded Beam Row 15
4. Summary and Discussion 16
Chapter 3 18
Numerical Analysis of Tieback and Braced Excavations 18
1. Case 1 Introduction: National Taiwan University Hospital 18
1.1. Subsoil Conditions 19
1.2. Tieback Support System Arrangement 22
1.3. Construction Phases 24
1.4. Monitored Lateral Wall Movement 29
1.5. Monitored Ground Settlement  29
1.6. Monitored Tieback Loads 30
2. Finite Element Model 31
2.1. Soil Input Parameter Determination 31
3. Structural Input Parameters 35
3.1. Diaphragm Wall Input Parameters 35
3.2. Tieback Free Section Input Parameters 35
3.3. Tieback Fixed Section Input Parameters 36
4. Finite Element Mesh 36
5. Construction Sequence 38
6. Wall Deformation and Ground Settlement 39
7. Tieback Free Section Loads 42
8. Tieback Fixed Section Loads 48
9. Fixed Section Ground-Grout Interface Mobilised Shear Strength 51
10. Case 2 Introduction: Neihu Cathay Life Insurance Office Building 55
10.1. Subsoil Conditions 55
10.2. Braced Support System Arrangement 58
10.3. Construction Phases 59
10.4. Monitored Lateral Wall Movement 62
10.5. Monitored Ground Settlement 62
10.6. Monitored Strut Loads 63
11. Finite Element Model  67
11.1. Soil Input Parameter Determination 67
12. Structural Input Parameters 69
12.1. Diaphragm Wall Input Parameters 69
12.2. H350×350×12×19 Strut Input Parameters 69
13. Finite Element Mesh 70
14. Construction Sequence 72
15. Wall Deformation and Ground Settlement 72
16. Strut Loads 76
17. Summary and Discussion 79
Chapter 4 80
The Impact of Pre-stressing Supports in Deep Excavations: A Parametric Study 80
1. Variation of Mobilised Shear Strength at the Fixed Section Ground-Grout Interface 80
2. Variation of Fixed Section Length with Pre-stress 91
2.1. The Effect of Pre-stress on Diaphragm Wall Displacement, Ground Settlement and Basal Heave 105
3. Plastic Failure Point Distribution and Incremental Displacement with Variations in Pre-stress – NTUH Tieback Excavation Case 112
4. Plastic Failure Point Distribution and Incremental Displacement with Variations in Pre-stress – CLIB Braced Excavation Case 120
5. Discussion 130
Chapter 5 132
Conclusions and Future Research 132
1. Conclusions 132
2. Future Research 133
References 134
Appendix A 137
Appendix B 138
Appendix C 164
Appendix D 184
Appendix E 209
Author Profile 227
                                

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