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This book presents the latest experimental and numerical analysis work in the field of ground deformation and base instability of deep excavations in soft clay subjected to hydraulic uplift. The authors’ latest research findings, based on dimensional analyses, well-instrumented full-scale field tests, systematic coupled-consolidation finite element analyses and centrifuge tests are reported. This book shows how to systematically approach a complex geotechnical problem, from identifying existing problems, reviewing literature, to dimensional and numerical analyses, validation through full-scale testing and centrifuge model testing. The methodologies are also introduced as major tools adopted in geotechnical research.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Introduction

Abstract
In recent decades, significant economic development in mega cities is driving the expansion of traffic demand, especially underground transportation. A large number of deep excavations have been carried out for underground metro stations.
Yi Hong, Lizhong Wang

Chapter 2. Literature Review

Abstract
For deep excavations in soft clay with an underlying aquifer, there are three major concerns: excavation-induced ground deformation, soil-structure interaction and base instability due to hydraulic uplift. In this chapter, previous studies on these three aspects are reviewed. More importantly, major short-comings of previous works are indentified
Yi Hong, Lizhong Wang

Chapter 3. Field Investigation of a Multi-propped Excavation in Soft Clay

Abstract
In recent decades, significant economic development in big cities such as Shanghai is driving the expansion of traffic demand, especially underground transportation. A large number of deep excavations have been carried out for underground metro stations. One major concern relating to excavations in urban areas is the possibility of excessive ground deformations induced by excavation. Based on the field monitoring of six multi-propped excavations in Shanghai, the characteristics of wall deflections and ground surface settlements in Shanghai soft clays have been summarised by Wang et al. (2005).
Yi Hong, Lizhong Wang

Chapter 4. Numerical Analyses of the Multi-propped Excavation in Soft Clay

Abstract
In the previous chapter, a case history of a multi-propped excavation in a greenfield site in Shanghai soft clay is comprehensively documented. Together with the case history documented in this study and eight others reported in the literature (Liu et al. 2005; Wang et al. 2005; Tan and Wei 2011; Liu et al. 2011), it is found that excavation-induced ground deformation in Shanghai soft clay is relatively smaller than similar excavations in soft clay worldwide (Long 2001; Moormann 2004).
Yi Hong, Lizhong Wang

Chapter 5. Dimensional Analysis of Excavation in Clay Subjected Hydraulic Uplift

Abstract
As summerised in Chap. 2, accidents and catastrophic basal failure associated with hydraulic uplift are reported worldwide from time to time (Milligan and Lo 1970; Moore and Longworth 1979; Ramaswamy 1979; Clough and Reed 1984; Davies 1984; Qu et al. 2002; Gue and Tan 2004). Concern on potential base instability due to hydraulic uplift is also raised in the case history reported in Chap. 3. In spite of the frequently encountered base instability due to hydraulic uplift, this subject has not been studied systematically and well understood. To assist with systematic study of this subject, dimensional analysis is carried out in this chapter to propose key variables (expressed in dimensionless groups) to be considered in this study.
Yi Hong, Lizhong Wang

Chapter 6. Centrifuge Modelling of Multi-propped Excavation in Clay Destabilised by Hydraulic UpliftHydraulic Uplift

Abstract
In this chapter, fundamentals of centrifuge modelling technique are introduced. Centrifuge test program and objectives of the tests are presented. Then a new experimental setup developed for in-flight simulation of multi-propped excavation in soft clay destabilised by hydraulic uplift is described in detail. Finally, a description of model preparation and experimental procedure is given.
Yi Hong, Lizhong Wang

Chapter 7. Finite Element Analyses: For Back-Analysis and Parametric Study

Abstract
The previous chapter describes centrifuge modelling of multi-propped excavation in soft clay destabilised by hydraulic uplift . As centrifuge tests in clay are rather time consuming and relatively costly, only limited numbers of centrifuge tests are carried out in this study. Systematical study on the initiation and failure mechanism of base instability due to hydraulic uplift relies on three-dimensional, coupled consolidation finite element analyses.
Yi Hong, Lizhong Wang

Chapter 8. Interpretations of Measured and Back-Anlaysed Results of Centrifuge Tests

Abstract
This chapter reports and compares measured results of two centrifuge tests (as described in Chap. 6) and back-analysed results of the centrifuge tests by three-dimensional coupled-consolidation analyses (as described in Chap. 7). The physical and numerical investigation aim at studying (a) the initiation and failure mechanism of base instability due to hydraulic uplift ; (b) base stabilisation effect of ‘anti-uplift piles’ installed inside excavation . Moreover, numerical parametric study was carried out to investigate effect of embedment depth of ‘anti-uplift piles’ on effectiveness of base stabilisation.
Yi Hong, Lizhong Wang

Chapter 9. Numerical Parametric Study

Abstract
In Chap. 8, the initiation and failure mechanisms of excavation subjected to hydraulic uplift are investigated by carrying out two centrifuge tests and numerical back-analyses. In spite of the reported initiation and failure mechanisms, the conclusions may be limited to the geometry of excavation and undrained shear strength of clay (c u ) modelled.
Yi Hong, Lizhong Wang

Chapter 10. Conclusions and Future Work

Abstract
Major objective of this research is to investigate ground deformation, soil-structure interaction and base instability of excavations in clay subjected to hydraulic uplift. Three methodologies, namely field monitoring, centrifuge modelling and finite element analysis, are adopted.
Yi Hong, Lizhong Wang

Backmatter

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