Field and laboratory studies of 'short-term' earthworks failures involving the Gault Clay in West Kent.

An investigation into the factors involved in the pore water pressure and stability of earthworks in the Gault is presented. The study is based on field measurements in cuttings and natural slopes, and on instrumented full scale embankment and cutting trials. many of the characteristics displayed by the Gault is attributed to its sedimentary and postdepositional history and so an outline of the geologic history of the strata and its engineering significance is presented, Details are given of the nature and widespread occurrence of Pleistocene periglacial discontinuities and their implications on the stability of earthworks are discussed. The trial embankment data includes the pore water pressure details before and during construction and the results of insitu permeability tests. The embankment failed during construction as expected and the contribution towards instability made by pre-existing slip surfaces in the foundation are elucidated. The cutting trial data includes the pore water pressure and ground displacement measurements made before, during and after the excavation of the cutting. Details are given of the stability of the steeply inclined section of the slope which failed 15 weeks after construction. Examples of cutting failures which occurred after a. much longer period are presented in the discussion of the Maidstone By-Pass investigations. The analyses of these failures and the recorded lateral slope displacements give an insight into the significance of progressive failure in the stability of the slopes, Post-failure movement of the slipped masses provide some data, on the shear strength mobilized along slip surfaces under low effective normal stresses