Experimental Research On Tensile Behaviors Of Cohesive Soil

Although tensile failure in soil has already became an essential issue in geotechnical engineering, the fact that the magnitude of soil tensile strength is so small and the lack of research data lead to a general understanding that the soil can not bear any tensile stress in practical engineering. In recent years, with rapid development of economy, national infrastructure and city construction is gradual developing, more and more engineering problems concerning the tensile strength of soil are presented, such as ground fracturing, core wall cracking, hydraulic fracture. Therefore, the research on tensile behaviors of soil not only helps to complete the theory of soil strength, but also to solve the complicated actural geotechnical problems.This paper has reviewed experimental methods of tensile strength of cohesive soil and developed a new piece of strain-controlled tensile equipment. With this equipment, uniaxial tensile test, one cyclic loading of uniaxial tensile test and two cyclic loading of uniaxial tensile test were performed on remodeling cohesive soil. Main achievements presented as follow:(1) The strain-controlled tensile equipment was developed on the basis of the existing triaxial apparatus. This new apparatus has good integrity and loading controlled, which can be used to obtain a more accurate stress-strain curve.(2) The tensile stress-strain curves under various conditions were presented. There are two types of uniaxial tensile stress-strain curves, representing two types of damage: A-type (brittle failure) and B-type (plastic failure). The peak strain increased with the increasing of dry density and moisture content. Stress and strain relation under cyclic loading was coincident with the uniaxial tension, with obvious hysteresis loop and residual deformation, indicating that such tensile deformation includes both plastical and elastic deformation.(3) The influence of dry density and moisture content on the tensile strength of cohesive soil was discussed. The tensile strength increases with the increasing dry density, while the tensile strength decreases with the increasing moisture content. As the moisture content gets higher, the influence of moisture content on tensile strength decreases. Meanwhile the empirical formula of the two factors and the tensile strength was obtained by linear regression.(4) The impact of the cyclic loading times on the tensile strength of cohesive soil was discussed. The variation of the tensile strength under cyclic loading was coincident with the uniaxial tension.The tensile strength increases slightly with the increasing of cyclic loading times, which meant cyclic loading has little effect on the tensile strength of cohesive soils.(5) From the microscopic aspect of the clay particles, the mechanism of the effects of dry density, moisture content and cyclic loading the times on tensile strength of cohesive soil were investigated.