Rheological characteristics of soft rock structural surface

There are two mechanisms of the coarse surface asperity resistance effect and rubbing resistance effect in the course of the soft rock structural surface creep, of which the former plays a dominant role in hindering the deformation in the starting creep phase, so that the structural surface creep usually displays the strong surface roughness effect, and so does the latter when the asperities in the coarse surface were fractured by shearing. Under the low stress condition, there are only two phases of the decelerating creep and the constant creep for the soft rock structural surface, and as the stress increases and overcomes the rubbing resistance, the accelerating creep failure of the structural surface will happen suddenly. Therefore, a multiple rheological model, which combines the nonlinear NEWTON body (NN) of a certain mass and the empirical plastic body (EM) with the classical SAINT VENANT body, NEWTON body, KELVIN body and HOOKE body, could be used to comprehensively describe the creep characteristics of the soft rock structural surface. Its mechanical parameter values will vary owing to the different surface roughness of the structural surface. The parameters of GH, GK and ηL are positively linearly correlative to the surface roughness. The surface roughness and m are negative exponential function correlation. The long-term strength τS is positively correlative to the surface roughness.