Title : Numerical modeling for undrained shear strength of clays subjected to different plasticity indexes

Page : PP.91-100

Author(s) : I-Hsuan Ho and Chung-Ching Hsieh

Keyword : Plasticity index, Modified Cam-Clay model, modified Drucker-Prager model/Cap model, overconsolidation ratio

Abstract : 

The presence of clay plays a significant role in how it affects the overall engineering behavior of the soil. Hence, the strength of the soil is governed by the clay, especially for the clay with very low strength. Therefore, engineers are required to figure out an appropriate strategy to deal with the engineering problems related to the soil containing the soft clay. It is important to understand the behavior of the clay and make the stress-strain behavior predictable. This paper presents the mechanical behavior of the clay subjected to various plasticity indexes (PI) under different confining pressures. The soil samples were taken from Hsin-Yi district of Taipei city in Taiwan. The Consolidated-Undrained (CU) triaxial tests were performed by controlling the initial void ratio, e = 1.25. The three different contents of Bentonite: 3 %, 6 % and 10 % were added in order to change the PI of the clay. Three different confining pressures of 50, 75 and 100 kPa, were applied in the tests. The overconsolidation ratios (OCR = 1.0, 1.25 and 1.5) were also controlled in each test. The undrained shear strength of the clay is therefore addressed based on different PI. Additionally, to investigate the applicable constitutive models for the clay, the modified Cam-Clay (MCC) model and the modified Drucker-Prager/Cap (MDP/Cap) model are employed in the ABAQUS finite element analyses to simulate the stress-strain behavior according to the circumstances created in the laboratory. The results indicate that the MCC model can fit the stress-strain curve better if the PI of the clay is relatively low. For a higher plasticity of clay, the MCC model will overestimate the strength. However, the MDP/Cap model can successfully capture the stress-strain behavior for a higher plasticity of clay. The applicability of these two models used to predict the mechanical behavior of the clay is addressed herein.

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