Simulation study on dilatant and rheologic properties of soft rocks surrounding deep roadway and its application

Surrounding rock deterioration，dilatancy and rheology are significant in deep soft rock roadways. Based on the incremental plastic flow theory and the rheological theory，a BVS model was established by connecting an im⁃ proved Burgers body，an improved viscoplastic body and a strain⁃softening plastic body in series，which can describe six mechanical properties of surrounding rock: strain softening， plastic dilatancy， three creep stages， steady and unsteady creep，rheological damage and rheological dilatancy. The three⁃dimensional incremental constitutive equations of the model were derived，and the numerical form that can be invoked by FLAC3D was developed. Combined with the parameter identification formulae derived from the three⁃dimensional incremental constitutive equations and the test data of rock samples from the Kouzidong Coal Mine，Xinji Mining Area，China，19 input parameters of the BVS model were identified. The test data，theoretical solutions and numerical results were mutually verified to strictly check the stress⁃strain response of each element under various loading conditions，each mechanical property，and whole model. The BVS model was applied to the numerical simulation of the 121302 headgate in the Kouzidong coal mine. The re⁃ sults show that the roadway disturbance is relatively weak. During the rheological period，the surrounding rock deterio⁃ rates in a large range，showing the characteristics of slight roof subsidence，shoulder corner coal dilatancy，whole wall inward migration and severe floor heave. The mining disturbance is significant， which induces the surrounding rock to deteriorate in a large range and the roadway section deforms strongly. The continuous heave of the floor mud⁃ stone drives the dilating bottom coal to squeeze into the roadway space， which is the main cause of the severe floor heave. The softening parameter directly caused by rheology at the depth of 1.5 m of the floor only accounts for 0-16% of the whole process，but the rheological damage causes stress adjustment，which indirectly leads an increase in the softening parameter. By comparing the numerical simulation results with the field measuring data，it is pointed out that the BVS model can basically describe the surrounding rock deformation and failure law of deep soft rock min⁃ ing roadways. However，there are still significant differences between them，and a further refinement of the BVS model is needed.