Coal-rock combination refers to the coal and rock as a whole, and the failure of the whole structure of the combination is the main cause for the instability of the deep underground engineering. In deep underground engineering, the coal-rock combination is usually under certain hydrogeological conditions, and it is prone to seepage and rheological failure instability accidents due to the long-term action of water and stress. In this study, the creep constitutive model of coal-rock combination considering the influence of moisture content was established based on the Burgers creep model. According to the experimental results of triaxial creep of rock, the relationship between the moisture content and the parameter of the Burgers creep model was derived, and the correctness of the constitutive model in this study was verified. Then, through the C++ language, the core equation of the model was modified, and the numerical calculation of the model was realized by introducing the coal-rock combination creep model considering the influence of moisture content into FLAC3D numerical simulation software. Finally, the model was used to simulate and study the creep characteristics of coal-rock combination with different moisture contents under triaxial loading. The results showed that the stress environment and moisture content have significant effects on the creep characteristics of the coal-rock combination. Under the same stress state, with the increased of moisture content, the strain rate of the coal-rock combination exhibited a non-linear rapid increase in the constant-velocity creep stage, the limit creep deformation and the instantaneous elastic deformation increased, and the viscosity coefficient was significantly decreased. For example, when the axial stress was 5 MPa and the moisture content increased from 0% to 1.5%, the strain rate increased by 44.06%, the limit creep deformation increased by 20%, the instantaneous elastic deformation increased 10.53%, and the viscosity coefficient decreased by about 50%. When the moisture content is 0%, the axial stress increased from 5 to 14 MPa, and the limit creep deformation increased nearly four times. With the increase of moisture content, this value will further expand. The research conclusions can provide a certain reference basis for the long-term stability control of surrounding rock in underground engineering affected by the water.

The mining pressure evolution of large mining height coal face with weak overburden under goaf is complicated, significantly influencing mining safety. This study uses the actual geological conditions of the II3 coal seam in Lingdong Coal Mine as research background. First, we combine the key layer theory and roof and floor lithology, the middle sandstone strata are determined as key strata. The fracture thin plate model for weak overburden with large mining height is established, considering elastic-plastic theory. We then obtain the calculation formula of key strata initial fracture span lo, periodic fracture span l₀, and front abutment stress. Second, the roof fracture and front abutment stress evolution during lower coal mining are obtained using the FLAC3D numerical simulation method. As the coal face advances, the immediate roof continues to collapse, and periodic fracture subsidence occurs. The coal face periodically appears, causing the phenomenon of roof subsidence acceleration, serious coal wall spalling, increasing pillar stress, and roof-stepped subsidence. The numerical simulation results show that the initial fracture span is approximately 25 m, and the stress of the key strata is approximately 12.5 MPa. The roof weighting span of the first cycle is approximately 2.39 m, the front abutment stress peak is approximately 14.33 MPa, and the influence range of the front abutment stress is approximately 17.50 m. Finally, comparing the numerical simulation results with the theoretical results shows that the evolution is similar, verifying the correctness of the mechanical model. The research results can predict the periodic weighting of overburden and provide a reference for the design of roof mining pressure control for large mining height coal face with weak overburden of lower coal seam.

With the continuous increase of mining depth and complex mining geological conditions, the mileage of roadways in underground engineering such as coal mine is increasing year by year. Complex conditions lead to different floor heave failure laws, and the control technology and strategy should be changed accordingly. How to evaluate the damage degree of floor heave under different conditions has become an urgent problem. Firstly, this paper makes a statistical analysis on the main evaluation indexes of the damage degree of roadway floor heave. Then, the fuzzy comprehensive clustering method is used to establish the classification method of floor heave damage degree, taking the floor heave amount, floor rock fragmentation degree, coal pillar size, buried depth, and floor lithology as evaluation indexes. The damage degree of floor heave can be divided into five types: light type, obvious type, severe type, destructive type, and extremely severe type. Finally, the rationality and accuracy of the method are verified by the measured value and evaluation value of No. 130203 roadway in the Zaoquan coal mine. The results can provide reference for the evaluation of the damage degree of the floor rock in similar condition mine and provide guidance for the design of the support and stability control of the failure of the roadway floor heave.