Study On The Calculation Method Of Foundation Stability Of New Buildings In The Old Mining Area

With the social development trend of urban centralization and the large increase of population,the construction land of many coal resource-based cities is facing an increasing gap.The goaf of coal mine goaf is huge,and the utilization prospect is broad.The rational utilization of the land resources in the old mining area has become a way to solve the shortage of construction land in mineral resource-based cities.It is of great significance for the sustainable development of local economy to change the surface land of the old mining area into construction land through the feasibility evaluation of the old mining area.For the new buildings to be built on the surface of the old mining area,the stability of the building foundation must be predicted and evaluated before the design.Due to the load of new buildings on the surface of the old mining area and many other factors,the original mechanical equilibrium state in the overburden of the old mining area may be broken,resulting in secondary "activation"-that is the residual movement and deformation of the surface,at the same time,the residual movement and deformation of the surface of the old mining area will have a negative impact on the stability of the surface buildings(structures),which will cause a malignant Cycle.However,the provisions related to the residual movement and deformation of the old mine area in the relevant regulations of our country are still not perfect.This paper mainly studies the influence of different foundation type selection on the stability of building foundation in the old mining area and the trigger discrimination of the load of new building on the surface of the old mining area on the residual movement and deformation of the surface,which has certain value for filling and improving relevant regulations and providing theoretical guidance for the actual project.Through the investigation of research data and practical projects at home and abroad,it is found that the additional stress of new buildings on the surface of the old mining area is one of the factors that induce the second "activation" of the old mining area.At present,most of the calculation methods of the influence depth used to determine the residual movement and deformation of the surface in the old mining area caused by the load of new buildings are based on the Boussinesq model,but the model fails to take into account the layered characteristics and vertical heterogeneity of the strata in the old mining area.When the Boussinesq model is used to calculate the influence depth of the load of the surface buildings in the old mining area,the influence caused by the change of the deformation modulus between the soil(rock)layers and the bulk density of the soil(rock)body is often ignored.The following are the stress concentration caused by the additional stress in the upper soft soil layer caused by the underlying hard rock layer and the stress attenuation caused by the lower hard rock layer,or the stress expansion caused by the additional stress caused by the underlying soft soil layer Scattered phenomenon.Therefore,the results obtained by using the traditional Boussinesq model are sometimes too different from the actual situation.When the local foundation soil layer is hard at the top and soft at the bottom,the calculation results of Boussinesq model tend to be larger;when the local foundation soil layer is soft at the top and hard at the bottom,the calculation results of Boussinesq model tend to be smaller in the part of the overlying soil layer,and the stress attenuation of the hard rock layer is ignored.These consequences may make the design scheme too conservative,resulting in waste of resources,and may lead to various kinds of hidden projects Suffer from.Therefore,the traditional Boussinesq foundation model used in the calculation of the safe depth of the building load in the old mining area can not meet the actual situation of the project.Based on the state space theory,this paper considers the influence of the change in the deformation modulus E of different soil(rock)layers in the strata of the old mining area on the depth of the additional stress of the building load.The transfer matrix method is used to establish the strip foundation,slab foundation,Independent base influence depth calculation model.According to the established mathematical model,a discrimination program was written with the help of Visual Basic software.The two methods of quantitative verification of model comparison and qualitative verification of FLAC3 D simulation were used to test the derived mathematical model and the prepared program.The results proved that the theoretical prediction model and calculation program are correct and generalizable in actual engineering.