Feasibility of measuring the undrained strength of peat in the direct shear box

Nur Aliaa, Binti Mohamad (2017) Feasibility of measuring the undrained strength of peat in the direct shear box. [Final Year Project Report] (Unpublished)

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Abstract

Direct shear test is the most common test to determine the soil shear strength. However, direct shear test can be used only to measure the drained strength of soil. If there is a limited access to the undrained strength testing device for example triaxial test and direct simple shear test, what would be the solution for that. Therefore, this study emphasis on identifying whether conventional direct shear device can be operated to provide reasonable estimates of undrained strength of peat. Due to the simplicity of direct shear testing, the feasibility of this device is tested in estimating the undrained strength of peat using variables of displacement rates. A comprehensive methodology is performed especially for soil classification test such as Von Post test, moisture content, organic content, fibre content and specific gravity. Then, the main test of this study which are consolidation test and direct shear test is done by varying the t50 multiplier (time to achieve 50% consolidation in conventional oedometer test). T50 value is used to determine the displacement rates of direct shear test. Direct shear test is then carried out as the rate of displacement for that particular t50 multiplier is calculated. Few parameters of shear strength can be obtained from the result of direct shear testing. For example, shear stress, shear strain, volumetric strain and shear strength ratio under variable displacement rates. From the findings of this study, the smaller the t50 multiplier, the faster the displacement rates. It is possible to measure the undrained strength of peat by performing the direct shear test with fast displacement rates. It is found that the undrained condition happened at 0.1t50 with displacement rates of 9.367 mm/min and shear strength ratio is noted as 0.48 which is falls in between the range of 0.38 - 0.55 for direct simple shear of peat. Such estimates of undrained strength may be useful in engineering practice when access to other shear strength testing device is limited. These findings from the study could also enhance the understanding of shear strength of remoulded peat

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