Study on evaluation method of foundation stability in small kiln goaf based on limit equilibrium method

The development and utilization of urban construction on the surface of coal mine goaf has become an effective way to solve the shortage of construction land index in domestic mining cities. In order to provide the basis for urban construction planning and ensure the safety of the proposed building, first of all, it is necessary to evaluate the foundation stability of the goaf site, and then according to the evaluation results, the treatment measures such as building, structure, foundation and goaf treatment can be taken. Among them, the small kiln goaf often becomes a suspended roof area due to its small mining area and insufficient roof caving. Under the action of surface building load, the suspended roof area may have sudden goaf collapse geological disasters, thus endangering the safety of surface buildings and personnel. Limit equilibrium method is one of the commonly used methods to evaluate the stability of foundation in small mine goaf. This method obtains the critical burial depth by establishing the equilibrium equation between roof pressure, building base pressure, self-weight of overlying strata and friction resistance of rock mass. However, there are still differences in the understanding of the concepts of base pressure p and burial depth H parameters in the calculation formula of critical burial depth of small kiln goaf, which leads to the non-uniqueness of calculation results and evaluation conclusions in the evaluation work. The problems existing in the formula are analyzed, and two modified calculation models corresponding to different concept understandings are established. After comparative analysis, it is suggested that the second modified calculation model with stronger applicability should be adopted, and the basic concepts of parameter p and H are clarified, that is, the meaning of parameter p is the average pressure of building basement, and the meaning of parameter H is the burial depth of goaf calculated from building basement. On this basis, the calculation formula of the critical burial depth of the goaf in the second modified calculation model is improved and extended for the bare and covered bedrock sites, so as to provide a reference for better guiding the evaluation of the foundation stability of the small kiln goaf.