INFLUENCE OF WATER CONTENT ON THE SHEAR STRENGTH PARAMETERS FOR COHESIVE SOIL

A laboratory program was performed for soil located in the Nile Delta in Egypt to study the shear behavior of cohesive soils in the range of plasticity. The soil's optimum water content was calculated. Also, the index properties (liquid limit - plastic limit - soil specific gravity) were determined. Then, seven direct shear tests and seven unconsolidated undrained Triaxial tests were done on compacted samples with loads from 100 to 400 kPa at the optimum moisture content (WcB = 18.20%) to define the shear strength parameters, at the dry side of optimum (Wc = 12.20% and 15.20%) and the wet side of optimum (Wc = 21.20%, 24.20%, 28.00%, and 35.00%). The shear box and triaxial tests were used at each water content to calculate the cohesion value and the internal friction angle. The results were compared, and A relationship was found between water content with the internal friction angle and the water content with the Cohesion. The findings demonstrate that raising the water content reduces the friction angle. Increasing the water content causes the Cohesion to rise till reaching the maximum value at the optimum moisture content. Then, the Cohesion decreases by increasing the water content till it reaches the minimum value. The Cohesion results in the direct shear test are less than in the triaxial test by a ratio from 3.00% to 14.00%. The internal friction angle in the direct shear test is less than in the triaxial test by 1.00 to 2.20 degrees.