Effects Of Matric Suction On The Shear Strength Of Highly Plastic Compacted Clay

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Jad Almula, Omaima Abdin Abdulaziz
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The objective of this research is to furnish extensive review of the principles of unsaturated soil mechanics with special emphasis on the shear strength of unsaturated soils and to study the effect of matric suction on the shear strength of unsaturated highly plastic clays which are dominant in Sudan. A comprehensive literature review on the gradual development of unsaturated soil mechanics emphasizing on effective stress, soil suction and shear strength theories was given. A higly plastic unsaturated clay soil from Al Damazine with plastic limit of (26-27) % , L.L (55-56)% and average optimum moisture content of 22% was selected for this research to study the effect of matric suction on the shear strength. Matric suction and shear strength were independently measured using the filter paper method and drained shear tests conducted in the conventional shear box apparatus respectively. The tested samples were prepared at different moisture contents covering dry & wet of optimum range (18, 20, 22, 25& 28%) using a constant dry density of 1.48 gm/cm3 for all tests mainly to study the effect of variation of air and water phases (matric suction) on shear strength. The shear strength was found to increase as matric suction increases following a bilinear relationship and reaching a maximum value of 273.76 kPa for a matric suction value of 5780 kPa and normal stress of 200 kPa. The rate of change in shear strength relative to change in matric suction was found to be affected by the air entry value of the soil where found to be for this particular soil type within the range of 600 to 700 kPa.
Matric Suction , Shear Strength,Highly Plastic Compacted Clay