Abstract：Red sand silty clay is used widely in highway engineering in Hunan Province. The direct shear tests on red sand silty clay with various geosynthetics were carried out to investigate the strength and deformation performances，the influence of parameters such as reinforcement layers and modulus，soil compactness，as well as confining pressures of test. Results show that with increasing compactness，the shear strength of soil increases significantly，but this is mainly caused by cohesive forces，which will disappear gradually with shear displacement increasing，and usually the stress-strain curve of red sand silty clay has a strain-softening phase. Reinforcement improves the stress-strain behaviors of red sand silty clay that both the peak strength and residual strength are increased，but the most important is the amount of reduction of residual strength，and the peak shear strength arrives at a larger shear displacement；as a result，the soil becomes more ductile. Based on the test results，the mechanism of the shear strength of reinforced soil is proposed tentatively；and the role and function of reinforcement in the stress-strain behaviors are also illustrated.
