| Abstract: |
Unsaturated soils are defined as soils which had a degree ofsaturation lower than hundred percent. The most important problemassociated with these soils is the variation of its shear strength withchange of suction. The measurement of shear strength parameters of”\unsaturated soils in triaxial apparatus requires some modifications inthe apparatus and high technique beyond those found necessary forsaturated soils. This study is primarily concerned with measuring thechange of shear strength parameters of unsaturated soils with suctionchange, using a modified triaxial apparatus.To achieve this objective, the conventional triaxial cell is modifiedso as the soil suction in three different elevations, (near the base, in the midheight, and near the top surface), of the sample can be measured.These measurements are carried out by the use of three miniaturetransducers imbedded into the soil specimen. Four groups of samples,(38.2 mm diameter by 80.0 mm height), with four different degrees ofsaturation, which equal to 100%, 85%, 75% & 70%, are tested usingthe modified system. The effect of strain rate, confining pressure, porewater pressure gradient, and degree of saturation on the shear strengthof saturated and unsaturated soils are experimentally investigated.Results indicate that a great variation of shear strength parameterswith suction is recorded. A call is made for controlling ’the testconditions, such as strain rate, confming pressure, and suction value, inorder to simulate the field conditions. This would ensure that themeasured shear strength parameters actually represent the fieldstrength. Another call is made for incorporating soil suction in thepractical applications, such as bearing capacity calculation and slopestability for the cases in which soils are unsaturated.
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