Shear strength of compacted soils

The main aim of this project was to study the shear strength behaviours of compacted soils from Bukit Timah Granite in Singapore through direct shear tests. The soils were compacted at various water contents and under two compaction efforts, standard Proctor and modified Proctor. Compaction procedures followed the ASTM D698 (2012) and ASTM D1557 (2012). Five water contents were chosen for each compaction effort to obtain compacted samples from dry to wet of optimum water content. Direct shear tests were conducted for both compacted and inundated samples. Results obtained from the experiments were analysed and discussed to study the relationships between shear strength, net normal stress, matric suction, friction angle as well as cohesion. The effective friction angle and effective cohesion determined by direct shear tests on inundated samples were studied and used to interpret the shear strength obtained for compacted soils to further understand the shear strength equation proposed by Fredlund et al (1978). Key findings of the study were that an increase in net normal stress causes an increase in shear stresses for compacted samples. Compacted samples prepared by modified Proctor effort had higher shear strength as compared to samples prepared by standard Proctor effort especially on the wet side of optimum. Effective friction angle and effective cohesion for each water contents were obtained on inundated samples. Values of effective friction angles and effective cohesion were used to determine total cohesion of compacted soil. It was concluded that matric suction only decreases at a high enough net normal stress as higher net normal stress would lead to a decrease in matric suction.Bachelor of Engineering (Civil