Modelling of consolidation behaviour of soil

Abstract

Routine laboratory consolidation test, though simple in procedure, involves a long time (about a week) and hence cost. Also, the determination of parameters for estimation of settlement and rate of settlement is tedious. After involving such time and effort, the amount of total settlement and rate of settlement estimated from test data vary significantly from field observations. It was, therefore, envisaged that use of the one-dimensional test with a pressure increment ratio larger than that used in conventional tests (thereby reducing the load steps, and time) together with a suitable mathematical model may produce the settlement information of a soil layer for a lesser time and effort. The model will also facilitate implementation of computational methods such as finite element method in settlement estimation. With these objectives, a simple mathematical function is proposed that can represent the void ratio - time relations (or dial reading - time relations) observed in a one dimensional consolidation test .on clay soil. The model consists of three parameters. The role and physical significance of each parameter is explained. To verify the effectiveness of the model, consolidation tests were performed on specimens from soil cakes reconstituted in the laboratory under two different vertical pressures (50 kPa and 100 kPa). Tests were performed with pressure increment ratios of 2 (used in conventional tests) and 4. The nature and amount of variation of the model parameters were determined from these tests. Comparison of e-t, e-cr' relations from test data and that back calculated using the model showed reasonably good agreement testifying the effectiveness of the model. It was observed that there is virtually no effect of using a pressure increment ratio of 4 instead 2 on the model parameters. Therefore, it is suggested that routine consolidation tests may be performed with a larger pressure increment ratio, especially in cases where the range of pressure to be investigated is large, together with the model without sacrificing accuracy. The values of Cv at intermediate pressure levels can be obtained from the model.