Safety analysis of building foundations over old goaf under additional stress from building load and seismic actions

Additional displacement of the building foundations over old goaf are prone to happen under the additional loads induced by new buildings, weakening-rock mass by mining and seismic actions, which will cause serious damage to the buildings. In order to analyze the safety of the building foundations safety over the old goaf, the structure characteristics of the strata over the old goaf was investigated and the instability conditions of overhanging rocks upon old goaf were also analyzed in this paper. The results indicate that the stability of overhanging rocks is remarkably decreased by the interactions of mining fractures, earthquake force and building load, in addition, the settlement of the foundations over old goaf is increased by the instability of overhanging rocks. According to the location of a new power plant in Yima Mine and its ambient conditions, we defined the influence scope of old goaf via resistivity tomography. Based on the seismic parameters of the construction site, a numerical FLAC3d model of the building foundation under the seismic actions and building load was developed. The numerical results are obtained as follows: the foundation of the main power house meets the requirement of 6° seismic fortification intensity; however, under 7° seismic fortification intensity, the maximum differential settlement of foundation between the neighboring pillars is close to the maximum allowable value, while the seismic fortification intensity reaches 8°, but the safety requirements will not be satisfied.