1.3 Organisation of Report

This research is mainly focused on the centrifuge model study of deep excavation to investigate the behaviour of support system and retained soil. Literature review of past research works on deep excavation with special emphasis on the behaviour of retained soil and the associated ground movement are given in Chapter 2. Previous centrifuge studies of deep excavation are also reviewed in detail:

In Chapter 3, the design of the centrifuge model and the test set-up are described. The system to simulate in-flight excavation and installation of lateral slabs are presented. The techniques for the visualisation of ground movement during test are also presented.

The results obtained from the first series of centrifuge tests on the behaviour of deep excavation reaching limiting equilibrium state are presented in Chapter 4. The tests conducted include (a) excavation supported by unpropped diaphragm wall, (b) excavation supported by diaphragm wall with one level of strut and (c) excavation supported by diaphragm wall with two layers of struts.

In Chapter 5, the results of three centrifuge tests conducted to study the behaviour of an excavation well before failure are presented. The soil in this series was subjected to 24 hours of high-g consolidation to obtain a soil stiffness profile increasing linearly with depth. The excavation depth of these tests was 50 mm. The long term behaviour of an excavation was also monitored.

Chapter 6 reports the finite element analyses (FEM) carried out on the excavation tests conducted using the Critical State Soil Mechanics Program (CRISP). In the analyses, modified Cam-clay model was employed to back analyse the centrifuge model tests data. By comparing the differences between the FEM and the test results, the problems in the existing FEM to predict the ground movement especially the soil settlement behind retaining wall, are highlighted. The effects of soil model and interface condition on the prediction of behaviour of deep excavation by FEM are also examined.

In Chapter 7, the conclusions of the present study are presented. The results from centrifuge tests and the finite element analyses on excavation as well as their comparisons are summarised. Some recommendations for further research on the topic under study are also given.