Mechanical characteristics of plane strain unloading conditions with different initial states

For the plane strain unloading issues in loess engineering, the lateral unloading plain strain tests on the loess with various initial states (intact, remolded and saturated) under different confining pressures and water contents are carried out by using the modified true triaxial apparatus. The stress-strain evolution, intermediate principal stress characteristics and strength characteristics of the loess with different initial states under unloading stress path are revealed. The study shows that the stress-strain relationship curves of the loess with different initial states exhibit ideal plasticity under low water content and low confining pressure, and change from weak one to strong one with the increase of confining pressures and water contents. The different initial states of the loess have great influences on the evolution characteristics of stress-strain relationship. The stress-strain curves of the intact loess are the highest, followed by those of the remolded loess and saturated loess. The higher the confining pressure and the lower water content, the greater the slope of the initial tangent, the higher the stress-strain curve and the greater the soil strength. The intermediate principal stress and the intermediate principal stress coefficient of the intact and saturated loesses first decrease and then increase, with a large attenuation range and a small growth range. The growth range of the intermediate principal stress coefficient is greater than that of the intermediate principal stress. The intermediate principal stress and the intermediate principal stress coefficient of the remolded loess first decrease and then remain stable. Under the plane strain unloading, the cohesion and internal friction angle of the loess with different initial states decrease approximately linearly with the increase of water contents. The influences of different initial states on soil cohesion are significantly greater than those of internal friction angle. The intact loess forms obvious lateral slip failure along the shear band under low confining pressures and low water contents, and the lateral dilatancy failure occurs under other conditions.