Abstract
To examine the applicability of an isotache model, two types of consolidation test were carried out: constant rate of strain (CRS) by changing the strain rate during the test, and an incremental loading (IL) test with small incremental ratios. It is found from the CRS tests that the stress shift caused by the strain rate change is nearly the same for all tested soils, but the behaviour after the change is different: some soils do not follow the isotache model. After selecting two typical soils (one follows the isotache model and the other does not), IL tests with various increment ratios and different durations at the loading stage prior to the incremental load were carried out to investigate how these parameters affect the strain–time relation. It is revealed that the strain–time relation is strongly governed by the magnitude of stress increments; in cases of small increments, most of the settlement is generated after the end of the primary consolidation. It is found that most test results can be interpreted by the isotache model. However, when the load duration at the loading stage prior to the incremental load is longer, the time–strain behaviour differs from that predicted by the isotache model.
Highlights
The Terzaghi type of consolidation theory is widely employed for the calculation of ground settlement in practice, assuming that a volume change of soil is caused only by increasing effective stresses – that is, the dissipation of the excess pore water pressure
The volume change is derived from the e–log p (e: void ratio; p: pressure) curve measured by an incremental loading (IL) oedometer test where the incremental load ratio (Dp/p) is 1, and its duration at each loading stage is 24 h
As a powerful concept to solve the settlement problems, attention has recently been paid to the isotache model, where the strain–stress relationship is governed by the strain rate
Summary
The Terzaghi type of consolidation theory is widely employed for the calculation of ground settlement in practice, assuming that a volume change of soil is caused only by increasing effective stresses – that is, the dissipation of the excess pore water pressure. In this conventional model, the volume change is derived from the e–log p (e: void ratio; p: pressure) curve measured by an incremental loading (IL) oedometer test where the incremental load ratio (Dp/p) is 1, and its duration at each loading stage is 24 h. The ground at this site consists of a single Holocene and several Pleistocene clayey layers, and a large discrepancy between the measured and calculated settlements was observed in the Pleistocene clayey layers
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