Abstract: Direct shear tests on a high purity Pakistan rock salt samples were performed by using a YZW100 direct shear testing device. The shear strength, shear deformation and failure mode of rock salt samples were analyzed. The results show that the shear failure mode of the salt rock is a ductile failure, and the shear stressdisplacement curve is in a gentle change with high residual stress which indicating the strong frictional resistance in the sample tested. Both the shear strength and the residual strength of rock salt samples increase with the increase of normal force applied. The tested cohesion of the Pakistan rock salt samples is 7.41MP with an internal friction angle of 44.1° while the tested residual cohesion is 0.16MPa, and the residual internal friction angle is 47.1°. Comparing with domestic stratified rock salt samples, the high purity Pakistani rock salt samples have similar internal friction angle, but higher cohesion and therefore a stronger shear strength. The shear failure plane of rock salt samples is not smooth and there are obvious local scratches observed, which is similar to the “furrow effect”. The test results have the reference value for the further understanding the failure mechanism of salt rock as well as the stability of the underground gas storage facilities.

Key words: rock salt, direct shear tests, shear deformation, shear strength