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 interac-tion,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 stud-ied.The experimental results show that the influence of matrix suction on the interface cohesion of unsaturated sand-structure inter-face 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 inter-face 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(δb)correspond-ing to matrix suction is little.Finally,a shear strength formula of unsaturated sand-concrete interface was established based on peak effect.
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