Abstract
This paper discusses the shortcomings of the traditional Coulomb shear criterion and the direct shear-box testing method used for clayey soil and presents a modified shear criterion that considers the elasto-plastic behavior of cohesive soil. This modified approach involves direct shear testing under constant volume, a method that has been developed by the author. A modified ring shear apparatus and the theory behind the shear criterion and its implication for slope stability analysis are then discussed and the results of investigated tuffitic clayey sediments are presented. The results show that the presented new shear criterion does not consider the cohesion as material constant, but rather it depends on the void ratio. In this case, the stress state and the consolidation status and thus the elasto-plastic behavior of the clayey soil are considered.
Highlights
Coulomb Shear Criterion is popular because it is simple and can be established by direct shear testing
The evaluation of the mechanical properties of soil has been primarily based on extensive laboratory tests, experience has shown in the past that shear strength parameters, as determined in standard laboratory tests, can lead to
The use of the cohesion in slope stability analysis determined in direct shear tests according to Coulomb shear criterion may lead to over estimation since it does not reflect the long-term true behavior of clayey soil
Summary
Coulomb Shear Criterion is popular because it is simple and can be established by direct shear testing. This criterion has severe shortcomings with regard to the behavior of cohesive soil, especially because it considers the cohesion as constant soil parameter. Prediction of the relevant behavior of soil and the evaluation of its properties are a prerequisite for examining the economy and safety of earth structures. (2016) Shear Failure Criterion and Constant Volume Ring Shear Testing Method for Clayey Soil. R. Azzam incorrect assessments of the stability of deep cut slopes in clays. Azzam incorrect assessments of the stability of deep cut slopes in clays In some cases, this discrepancy can be eliminated by changing the conditions under which the laboratory tests are being carried out
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