Study on numerical simulation of safety depth of goaf under expressway

In recent years, the engineering cases of expressway passing through the goaf are increasing gradually. When the buried depth less than a threshold, the external load of the expressway may spread to the underlying goaf, leading to instability of the overlying rock structure, and threatening the safety of vehicles. In order to ensure the safe operation of the expressway above the goaf, on the basis of considering the periodic cyclic dynamic loading characteristics of vehicle load. The disturbance depth of vehicle load under different embankment heights, pavement stiffnesses, vehicle loads and vehicle speeds is studied by employing numerical simulation experiments. The empirical expression of vehicle disturbance depth is obtained using multiple regression analysis, and then the determination of the safety depth of the goaf under expressway is proposed. The research results show that the load disturbance depth decreases with the increase of embankment height, pavement stiffness and vehicle speed, while the load disturbance depth increases with the increase of vehicle load. The disturbance depth has linear correlation with embankment height, and non-linearly correlation with pavement stiffness, vehicle load and vehicle speed. The residual error between the calculated value of empirical formula and the experimental value of numerical simulation is between 0.0～2.8 m, and the root mean square error is about 0.95 m. The safe depth of the goaf under expressway must be greater than the sum of the vehicle load disturbance depth and the water flowing fractured zone developing height. Finally, the researches are applied to Wuyun Expressway, the results show that the safety depth of the goaf under Wuyun Expressway should exceed 104 m, which is less than the buried depth of the shallowest goaf in the study area (158 m). That is to say, the external load of Wuyun Expressway will not lead to the instability of the overlying rock structure and activation of the underlying goaf.