This paper presents an analysis of the undrained expansion of a cavity in m
odified Cam clay. The problem is formulated in small strain in the elastic
zone and large strain in the plastic zone. Exact closed-form solutions of t
he effective stresses around the expanded cavity are presented. Closed-form
expressions for the excess pore water pressure and the total stresses have
also been derived based on a simplified assumption regarding the shear str
ess variation around the cavity. The analytical solution shows clearly the
influence of the overconsolidation ratio on the excess pore water pressure
induced by cavity expansion. As both the excess pore water pressure and the
cavity pressure are expressed explicitly in terms of the primitive modifie
d Cam clay parameters, the solutions may provide a theoretical basis for th
e interpretation of in-situ tests such as the piezocone test and the pressu
remeter test.