Rock parameters inversion for estimating the maximum heights of two failure zones in overburden strata of a coal seam

In order to enter effective parameters of rock mass in a numerical model, the relationships between mechanical parameters of rock and rock mass were obtained by an inversion method and an orthogonal test, given our measurements of the maximum heights of two failure zones in the Longdong coal mine. Using the maximum heights of the caving zone and the water-conducting fractured zone as test indices the modulus of elasticity, the Poisson ratio, cohesion and tension strength as test factors and different values of reduction enhancement factors as test levels, an orthogonal test was designed to obtain an optimum simulation scheme. From the analysis of different values of reduction enhancement factors which affect the test indices, an optimum factor combination for modification of parameters could be inferred. By using modified parameters in our numerical simulation, the maximum heights of the caving zone and the water-conducting fractured zone in the extensive Xiyi area were determined as 15.06 m and 36.92 m. These values were almost the same as those obtained by similar material simulation (8.5 m and 37.0 m) and empirical prediction (8.4 m and 34.4 m). These results indicate that the modification of parameters is a rational method.