Modification of unsaturated direct shear instrument and sand-structure shear test.

The study on the mechanical properties of soil-structure interface is the basis to solve the problem of soil-structure interaction, which involves many aspects of practical engineering. By modifying the conventional unsaturated direct shear apparatus and using the modified unsaturated direct shear apparatus, the shear tests of unsaturated sand-structure interface were carried out, and the effects of the matrix suction, the structural interface type and the net normal stress on the shear strength of the interface were studied. The experimental results show that the influence of matrix suction on the interface cohesion of unsaturated sand-structure interface is great, while that on the interface friction angle is small. With the increase of matrix suction, the shear strength of unsaturated sand-concrete interface increases first and then decreases, indicating a peak effect. The shear strength of unsaturated sand-steel interface was less affected by matrix suction. Under the condition of constant matrix suction, the shear strength of sand-steel interface increases nonlinearly with the increase of net normal stress. The influence of net normal stress on the friction angle (δ^b) corresponding to matrix suction is little. Finally, a shear strength formula of unsaturated sand-concrete interface was established based on peak effect. [ABSTRACT FROM AUTHOR]