Study on Constitutive Model of Muddy Soft Rock under Cyclic Shear

The frequent occurrence of microseisms in the reservoir area makes the muddy soft rock subject to cyclic shear dynamic action. Based on the fractional Nishihara model (FNM), the adhesive pot of Able is improved, and the constitutive model under the corresponding conditions is further obtained, which is verified by the cyclic shear test of the muddy soft rock sample. The research shows that: (1) the original FNM can be summed up as a special solution when the sinusoidal function (cyclic action) is zero in the proposed mode. (2) The model shows good applicability (R²∈ (0.96,0.98)), and the equation curve has the characteristics of “single and double turning points”, which can be found in the test. (3) The main influencing factor of the model is fractional order n, in which the stability condition n∈ (0,0.6), the failure condition n∈ (0.6,1.0). (4) With the increase of n, the shear modulus G and viscosity coefficient η decrease, which can better reflect the macroscopic phenomenon. (5) From the point of view of parameter disturbance, the irregular fluctuation of η with the increase of n in the previous literature is explained. The research results can provide theoretical reference for the long-term stability control of muddy soft rock slope under microseismic condition.