Experimental study on influence of stacking angle on bearing capacity of filling piers in gob

High-concentration slurry has the characteristics of environmental protection, energy saving, emission reduction, safety, and high efficiency. It is gradually being recognized and applied. After being injected into the gob, the supporting truncated cone is usually formed. Different stacking angles have different supporting effects on overlying strata.And it is important to grasp the influence of the stacking angle on the bearing capacity of the truncated cone. In order to study the effect of the stacking angle on the bearing capacity of the truncated cone,3D printing technology was used to make the mold. The cement was selected as the cementing material, standard sand as the aggregate, and the high-concentration slurry with the mass ratio of the cement and the aggregate of 1∶3, and the mass ratio of the water to the cement of 0.56 was prepared. The high-concentration slurry was poured into the mold to prepare truncated cone samples of different stacking angles. The high-concentration slurry was released after being allowed to stand in the mold for 1 day, and then the samples were placed in water for curing. When the 7 days was reached, the uniaxial compression test was carried out by a WAW-300 microcomputer controlled electro-hydraulic servo universal testing machine.The test results show that when the diameter and height of the circular truncated cone are the same, the smaller the stacking angle, the stronger the ultimate bearing capacity. The ascending phases of the force-deformation curves with accumulation angles of 30°, 45° and 60° are consistent with the stress-strain curve during the classical compression process. The failure process can be divided into I transient elastic phase，II fracture expansion phase，III maintenance structure failure phase.The pressure failure process of the cone-shaped specimens with different stacking angles are similar. Due to the surrounding material's protection of the core area, the confining pressure is provided, so that the smaller the stacking angle, the larger the confining pressure, and the more difficult it is for the cone-shaped sample to be damaged.As the packing angle increases, the bearing capacity per unit volume of the sample increases. Regardless of the layout design of the piers, only the arithmetic sum of bearing capacities of all piers is considered. Under the same amount of grouting, the larger the stacking angle, the better the bearing effect.