Study on bearing deformation characteristics and lateral pressure distribution law of caved gangue in gob

Under the load of overlying strata, lateral pressure from the caved gangue in gob will be exerted on the support body of gob-side entry retaining or coal pillar. As time goes on, lateral pressure may lead to instability of support body of gob-side entry retaining or coal pillar, and then induce surface collapse. In order to study the bearing deformation characteristics and lateral pressure distribution law of caved gangue in gob, a combined test device for bearing deformation of caving gangue that can measure lateral pressure is developed. The caved gangue with uniform particle size distribution of 5 − 30 mm is taken as an example. By setting the same total loading time (16 h), the same target load (10 MPa) and the different number of loading levels (1, 2, 4), the bearing deformation characteristics, lateral pressure distribution law and particle size change of caving gangue before and after test are studied. The test results indicated that: Along with the increase of axial load, the axial deformation of caved gangue increases gradually, the residual bulking coefficient and porosity decrease gradually, which are more obvious in loading stage than in constant loading stage. In the early constant loading stage, the axial deformation of caved gangue grows rapidly, and then tends to be slow and steady gradually, if no strain surge occurs, the relationship between strain and time meets the logarithmic relationship. With the same target load and total loading time, as the number of loading levels increases, the total strain generated in constant loading stage increases significantly, and is 3.02%, 9.07%, 17.72% respectively, which indicates that the total energy input of caved gangue decreases with the increase of loading level number, but it plays a significant role in promoting the sliding filling and structural adjustment of caved gangue. The lateral pressure coefficient of caved gangue increases obviously with the increase of load. Caved gangue body shows strong reduction effect of load transfer and the value of load acting on caved gangue body decreases progressively from top to bottom. In the process of bearing deformation of caved gangue, the total amount of caved gangue with 5～10 mm particle size is in dynamic equilibrium. The research results have certain guiding significance for mining subsidence control.