The two-way repeated loading of a silty clay
The main aim of the research was to study the behaviour of a silty clay under two-way cyclic loading. Equipment was developed for the application of a sinusoidally varying deviator stress to a sample in the triaxial cell. The equipment was designed to apply deviator stresses in both compression and extension during each cycle. ii A programme of monotonic and two-way cyclic triaxial tests has been performed on samples of Keuper Marl, isotropically consolidated to a range of stress histories. The build-up of strain and pore pressure during repeated loading is discussed. A model is developed, within the framework of the critical state theory of soil mechanics, to predict the amount of pore pressure produced by a given number of loading cycles at a known stress level. An extension of the model is suggested whereby the varied loading, more appropriate to offshore foundation conditions, may be analysed. In addition, a programme of monotonic and cyclic simple shear tests has been performed. The equipment has been developed, during the course of the research, to enable the direct measurement of pore pressure during shear. At attempt has also been made to monitor the change in lateral stress during shear by means of an instrumented membrane. The results of the simple shear tests have been analysed and are presented in terms of horizontal shear stress and effective vertical stress. An attempt has been made. to deduce the principal stresses present in a sample subject to simple shear loading and a method of relating the results from monotonic tests using simple shear and triaxial devices is discussed.