Abstract: Red clay is widely distributed in Southwest China. It has practical engineering importance to study the stressstrain characteristics of the compacted red clay. Both direct shear tests and triaxial shear tests were performed on a series of the compacted red clay samples with different moisture contents and degrees of compaction. Direct shear test results and triaxial shear test results on soils with the samples having the same degree of compaction were compared. The following conclusion can be summarized: The shear strength parameters increase with the degree of compaction and reduce with the moisture contents. Higher tested cohesion are occurred at higher moisture contents or higher degree of compaction. When the moisture content is lower than the optimum moisture content in the Proctor Test, it has more impact on the cohesion; whereas, when moisture content is higher than the optimum moisture content, it only has minor impact on the cohesion value. The shear strength of the compacted red clay is linearly proportional to the moisture content and the degree of compaction. Both direct shear test and triaxial shear test demonstrate similar trends with moisture content as well as the degree of compaction but the shear strength magnitudes are different. The cohesion value obtained from direction shear test is only 0.58 of the value obtained from triaxial shear test. The internal friction angle obtained from the direct shear test is 1.34 times of the value from the triaxial shear test.

Key words: Compacted Red Clay, Direct Shear Tests, Shear Strength, Cohesion, Internal Friction Angle, Moisture Content, Degree of Compact