Changes in Lateral Stress During Slurry Trench Wall Installation.

Abstract

The thesis is concerned with the effects of slurry trenching (diaphragm wall installation) in an overconsolidated clay, with particular emphasis on the changes in lateral stress which occur. A review of the literature on diaphragm wall installation in stiff overconsolidated clay was carried out, with particular reference to the measurement of changes in stress and the application of finite element analyses. The problem was investigated by means of centrifuge model tests and finite element analyses. The main body of the thesis details the development and results of a series of centrifuge tests. A model at 1 to 100 scale was tested at 100 gravities, enabling both the long and short term effects of slurry trench walling to be investigated. The technique adopted used a fluid-filled neoprene rubber bag in the place of the trench that was drained to ground level to simulate excavation under bentonite slurry. A mixture of plaster of Paris, iron-filings, fine sand and cement powder was then deposited into the bag to simulate wall placement. By using different fluid heights of different densities in the rubber bag, a series of initial earth pressure coefficients were modelled. The effects of both a stress and strain controlled boundary at the remote end of the model were also investigated. Finally, simulated concretes of different densities were adopted to see what effect this would have on placement stresses. A technique was developed to enable the measurement of changes in total lateral stress changes at up to 10 locations within the model. Pore water pressures were measured at the same positions, and ground settlements were measured at the surface of the model. A series of finite element analyses was carried out to extend the scope of the centrifuge model results by varying further the initial in situ conditions. The conclusions and suggestions for further work are presented at the end of the thesis.