Ground deformation associated with tunnelling and deep excavations in clay, with particular reference to London clay

Abstract

This work is mainly directed towards problems of ground stability and ground deformations caused by tunnelling and deep excavation in clay. The particular question of surface settlement associated with soft ground tunnelling has been critically examined. Derivation of semi-empirical relationships has facilitated settlement prediction. A detailed analysis has been carried out on the results of an extensive research programme of in-situ measurements aimed at determining ground movements created by a) hand excavation of a 4.146m diameter shield-driven tunnel at a depth of 29.3m below ground surface, and b) the excavation of a 6.1m long, 0.8m wide and 15m deep bentonite slurry-supported diaphragm wall. Both engineering structures were situated in the stiff fissured, over consolidated London Clay. The stress-strain regime around the tunnel and behind the diaphragm wall was examined, and a theoretical analysis was attempted in order to provide an explanation for the actual performance of both structures during the early stages of construction.