Stability of Axisymmetric Excavations in Clays

Abstract

Axisymmetric (shaft) excavations are quite common in the construction industry (e.g., inspection or access chambers and excavations for bored piles or piers). The stability of an axisymmetric excavation in clay with uniform undrained shear strength profile is reviewed. A wall failure mechanism is found to be the most critical when both wall failure and base failure are considered. Based on this, upper‐bound calculations are carried out for an axisymmetric excavation in clay with undrained shear strength varying linearly with depth. Stability charts are also presented for the critical wall failure mechanism. In normally consolidated clays, with zero shear strength at the ground surface, axisymmetric excavations are shown to be unstable if not supported. The width of the settlement zone adjacent to the excavation is found to be approximately equal to 0.4 times the depth of the excavation.