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In order to solve the problem of complex stress and instability in the intersection area of roadway under the condition of soft and hard interbed roof, taking 1113 three-fork roadway of Qiuji Coal Mine as the engineering background, the stress distribution law at the intersection is studied by theoretical analysis method, and the deformation and failure mechanism of surrounding rock is revealed; based on the strength strengthening theory of surrounding rock, thick anchor plate theory, integrated support theory and suspension theory, a combined support system of “anchor （cable）+anchor cable beam+steel mesh” is formed, and various key support parameters are calculated. The research results show that the acute angle triangle area of three-fork belongs to a high stress concentration area, and the surrounding rock of the roadway is easy to be damaged. The maximum damage depth is 2.77 m according to the theoretical calculation; under the control of combined support system, through numerical simulation verification, the maximum concentrated stress in the triangle area is 10.74 MPa, the maximum roof subsidence is 16.82 mm, and the maximum damage depth is 2.24 m, which can effectively improve the mechanical state of surrounding rock; after the site implementation, there is no obvious separation of the roof, meeting the safety needs.

In order to solve the problem of selecting reasonable blast hole spacing in gob-side entry retaining, based on the fracture forming mechanism of bi-directional shaped charge blasting, a mechanical model of combined hole shaped charge blasting is established, the influence parameters of shaped charge pipe are introduced, the rock crack propagation length after blasting is analyzed, and the calculation formula of blast hole spacing is deduced. Taking Qiuji Coal Mine as the engineering background, the reasonable blast hole spacing is calculated as 1.0 m. LS-DYNA software is used to simulate the crack propagation process of double hole shaped charge blasting with spacing of 0.8 m, 1.0 m and 1.2 m. The simulation results show that the peak stress of rock in the direction of shaped charge blasting is 2.6 times of that in the direction of non-shaped charge blasting at 0.2 m away from the center of the blast hole, and the crack in the direction of the connecting line of the blast hole is easier to expand; when the spacing of the blast holes is 1.0 m, the cracks between the two holes are completely connected and there is no vertical crack in the center of the connecting line of the blast holes. The field test in Qiuji Coal Mine shows that continuous cracks are formed in the holes after blasting with a spacing of 1.0 m, and the cracks between the holes are connected to form a cutting surface, which is consistent with the results of theoretical calculation and numerical simulation.

An improved method for rockbolt fracture is proposed in this paper to determine the exact fracture position of rockbolts simulated using cable structural elements (cableSELs) in FLAC3D. This method employs the total elongation of the free segment of the rockbolt as the fracture criterion. The maximum deformation position is identified by comparing the length of each cableSEL in the free segment, leading to the fracture. The simulation results validated through a rockbolt tensile test closely match actual conditions. The proposed method was used to optimize the roadway support in deep extra-thick coal seams (DECSs). Optimized parameters were obtained by simulating and analyzing different lengths and spacings of rockbolts and anchor cables. The field implementation conducted shows that the optimized deformation and support strength of the roadway meet safety needs. [ABSTRACT FROM AUTHOR]

In order to guide the model test fillers and improve the test accuracy, the mudstone similar material was selected to make samples, and the effects of three factors affecting the filling process of model test on the mechanical properties of mudstone similar material was studied. The analysis results show that when the number of layers increases from 1 layer to 5 layers, the uniaxial compressive strength, elastic modulus and tensile strength of similar materials are reduced by 23.80%, 32.0% and 20.83% respectively. And the compaction times are increased from 1 to 5 times, the uniaxial compressive strength, elastic modulus and tensile strength of similar materials increased by 15.00%, 28.61% and 6.76%, respectively. Compared with the interface treatment method of rough treatment, the uniaxial compressive strength, elastic modulus and tensile strength respectively increased by 14.25%, 22.63% and 7.99%when gypsum was sprayed on this basis. The multiple linear regression equation between the mechanical properties of similar materials and the influencing factors of packing process is established. Combined with the test results and equations, the model test fillers can be guided, the mechanical properties of similar material can be prevented from decreasing, and the test accuracy can be improved.

The safety production pressure in coal mines is huge, and there is a general phenomenon of over-supporting in roadways. Even hard and dense thick limestone roofs do not dare to be unsupported. 1102 track roadways of Qiuji Coal Mine is taken as the engineering background, by constructing a hard roof deformation analysis model, quantifying the role of the fifth layer limestone thickness in controlling roadway deformation, using numerical simulation to verify theoretical calculation results, using field test and monitoring reinspection research results. The research shows that as the thickness of limestone increases, the roof deformation decreases continuously and the self-stability of the roadway increases. When the thickness of the fifth layer limestone reaches 1.5 m, the deformation of the roof is reduced by 77.4% compared with the thickness of 0.2 m, and the plastic zone is reduced by 40.5%. The thickness of the fifth layer of limestone in 1102 track roadway is greater than 1.5 m. The scheme of without supporting in the roadway roof and the anchor net supporting on both sides of the roadway is adopted. The results show that the vertical convergence of the roadway is extremely small, and the convergence on both sides of the roadway is less than 15 mm. The cables on both sides of the roadway are under stable force. The roof force measuring bolt (cable) does not rise but falls back after applying the pre-tightening force and no cracks and separation can be seen in the roof peep to meet the safety requirements.

Take the background of hard roof support problem of Qiuji Coal Mine 1102 working face haulageway, the cantilever beam model of uncutting roadway roof and the deformation and stress model of gob-side entry retaining are established. The maximum cantilever length of roadway roof cantilever beam structure is 4.68 m by theoretical calculation; the support resistance of the roadway roof with unit length suspended is 166.74 kN. Based on this, the parameters of roadway are designed, the specification of constant resistance and large deformation anchor cable is determined as ?准17.8 mm × 10 300 mm, and the spacing of two columns of anchor cable to be 1 000 mm and 2 000 mm respectively, and the roadway mine pressure is monitored. Monitoring results show that: within the range of 75 m to 173 m from the open-cut hole in 1102 haulageway, the maximum displacement of roadway roof and floor is about 36 mm, the roof abscission layer occurs at the junction of mudstone and limestone, the accumulative amount of abscission layer amount is 25 mm, the maximum stress of roof anchor cable is 150 kN, both deformation and stress are within a safe range, meet the stability requirement of roadway.

Underground chambers and tunnels in different strata have different failure modes. In practice, stability evaluation of underground engineering should consider the surrounding rock creep properties. In this research, uniaxial and triaxial creep tests are performed to explore the mechanical and fracture behaviors of mudstone, sandstone, and limestone. The experimental results show that the fissure angle (α) has a great effect on the long-term strength (LTS) of sandstone and limestone, and their minimum values are observed when α = 75° and 45°, which are 26.7% and 25% lower than those of the corresponding intact samples, respectively. However, the fluctuation in the LTS of mudstone is less than 5.2%. The steady creep strain rate of fissured mudstone does not increase as significantly as that of sandstone and limestone, which increase more than 6 times when the deviatoric stress exceeds the LTS. As α increases, the failure modes of mudstone and sandstone change from mixed failure to tensile failure when α = 75°, and limestone samples mainly exhibit tensile failure. Limestone and sandstone are prone to shear failure under confining pressure and have higher degrees of internal crack development than mudstone. The dissipated energy of limestone is higher than that of sandstone and mudstone. A high dissipated energy ratio is closely related to a low LTS and tensile failure. Due to the small variation in the LTS of fissured mudstone, using LTS to judge stability is effective. For sandstone and limestone, the sudden increase in the steady creep strain rate can be an indicator for evaluating stability. [ABSTRACT FROM AUTHOR]