Experimental study on roughness and long shear strength of fracture rock

In order to analyse the long term behavior of rock mass and to reveal unstable failure mechanism of fractured rocks, experimental studies on the micro-structure fractured surface and micro-contacting evolution were carried out. The cubic specimens were sandstones with the side length of 50mm. Two types of rock fracture surfaces were made through direct-shear test and Brazilian split test. Three specimens were selected in each type to perform shear creep experiment. The roughness of fracture rocks was scanned by Laser Scanner and during loading process. The experimental results show that: ① in the shear creep process, the fracture surface becomes rough or smooth. ② There are two main mechanisms constitute long-term shear strength of rock fracture: one is the micro-asperities of the anti-cutting ability, the other is the macro-asperities of the anti-friction ability. Whatever failure mode,the two mechanisms combined effect on the rockiness in loading process, meanwhile they play different roles and convert to each other with time and shear displacement increasing.