Gangue paste material is mainly composed of coal gangue with particle size, which is mixed with cement. Fly ash and additives can be added to change its performance. In this paper, the influence of each component on the mechanical properties of gangue paste material was studied by an orthogonal experiment. The conversion relationship among various indexes of mechanical properties of gangue paste material and the response surface prediction model were discussed. The results show that the mechanical properties of gangue paste materials are positively correlated with the content of cement, the content of fly ash and the mass concentration, which increase with the increase of the three factors, and show the primary and secondary relationship of the content of cement > the content of fly ash > the mass concentration. A response surface prediction model of mechanical property parameters is established, which includes the first order term of the influencing factors of gangue paste material and the first order interaction term between any two factors. In the response surface prediction model of uniaxial compressive strength, splitting tensile strength, cohesion and elastic modulus, the goodness of fit test coefficients are 0.998, 0.957, 0.970 and 0.997, respectively, which proves that the model has good goodness of fit. The research results provide basic parameters for paste filling mining practice, and also provide the basis for numerical simulation of filling body value.
Bolt support is an economic method of roadway support. However, due to the influence of mining disturbance, the stress of roadway-surrounding rock changes, thus resulting in varying degrees of confining pressure in the radial direction of bolt. In this manuscript, a numerical solution was proposed to determine the largest confining stress in longitudinal tests of cable tendons. FLAC3D was selected to simulate the longitudinal process of cable tendons. The structural pile element was selected to simulate the cable tendon. The loading behavior of the cable was controlled by the cohesive and the frictional behavior of the cable/grout surface. To confirm the credibility of this numerical solution, the loading behavior of a normal cable and an improved cable was simulated. Experimental longitudinal tests were selected to validate the numerical results, showing that there was a satisfactory agreement between numerical and experimental results. The loading behavior of normal cables and improved cables was numerically simulated. Under the same test conditions, when the improved cable was used, the confining medium can generate much higher confining stress compared with normal cable tendons. Consequently, higher confining stress can result in a larger loading capacity of cable tendons.
To study the influence of filling step and advancing distance on the deformation and failure of a working face floor, a mechanical model based on elastic foundation beam theory is established. The deflection and bending moment curves of the floor under different filling steps and advancing distance are obtained by Maple. Then, a fluid–solid coupling model of paste-filling mining on confined water is established by FLAC3D. The effects of different filling steps and advancing distance on the floor displacement, stress, and plastic zone of the floor are analyzed. The results show that there is a “concave” quadratic relationship between the filling step and the maximum displacement of the floor, and there is a “convex” quadratic relationship between the advancing distance and the maximum displacement of the floor. The maximum stress of the floor increases linearly with the increase in filling distance and tends to be stable with the increase in advancing distance. Moreover, the increase in filling steps will lead to the continuous increase in longitudinal failure. This study could guide paste-filling mining above confined water.
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