Study On Stability Evaluation Of New Building Foundation In Subsidence Area Of Lugou Coal Mine

The continuous exploitation of coal resources has led to the continuous and large-scale increase of coal mining subsidence areas in China.At the same time,with the continuous advancement of China’s urbanization construction,there is a shortage of ideal engineering construction land.The contradiction between the subsidence area caused by coal mining and the decreasing area of engineering construction land is becoming increasingly prominent.Transforming the subsidence area into engineering construction land is one of the effective ways to alleviate the shortage of engineering construction land.In this paper,theoretical analysis,numerical simulation and field application are used to study the stability of the foundation of new buildings in the subsidence area of Lugou coal mine.The main conclusions are as follows:（1）The"mechanical model of mining overburden structure under load"is established by theoretical analysis method,The criterion of mining overburden sliding instability with the increase of load under the action of surface load is obtained,When the rotation angle and fragment size of articulated rock block comply with i<0.5sinθ₁ or i>sinθ₁,the possibility of instability of mining overburden structure gradually increases with the increase of surface load,When the rotation angle and fragmentation of articulated rock block meet 0.5sinθ₁<i<sinθ₁,the mining overburden will not rotate and lose stability with the increase of load.（2）3DEC numerical simulation software is used to study the migration law of mining overburden and the development characteristics of separation layer and vertical fracture.The failure movement of overburden is affected by hard rock layer and shows the characteristics of group movement.The development height of separation layer rises step by step with the advance of working face,and the development of separation layer becomes weaker with the direction away from the stope,Whether the broken rock blocks form masonry beam structure determines whether the rock stratum belongs to collapse zone or fracture zone.The vertical cracks show the characteristics of cracking first and then closing,and arch development gradually changes into saddle shape.（3）The stability of goaf is evaluated according to the relationship between load influence depth,mining overburden failure height and mining overburden structure stability evaluation method.The research shows that the failure height of mining overburden is 143.8 m,and the load influence depth of new buildings is 14.4 m,and the sum of the two is less than 355 m of the buried depth of the coal seam.The allowable building load of mining overburden structure is 2290 k Pa,and the average pressure of building base（80 k Pa）is far less than the allowable load.Therefore,it is determined that the goaf is in a stable state.（4）The probability integral method is used to predict the residual movement and deformation of the surface in the subsidence area.The maximum inclination value of the surface is 0.67 mm/m,the horizontal movement value is 105 mm,and the maximum horizontal deformation value is 1.03 mm/m.The surface movement and deformation meets the class I deformation standard,and it is judged that the subsidence area is in a stable state.On this basis,the analysis shows that the fault near the new building site has no effect on the residual deformation of the new building area.（5）PS-In SAR is used to monitor the new buildings and surface movement and deformation,and it is determined that the new buildings in the subsidence area of Lugou coal mine are in a stable state.Among them,the overall subsidence trend of the study area in one year from November 2020 to October 2021 is that the average settlement rate is mainly 0～20mm/a,and the monthly surface settlement is mainly-10～10mm,with an average value of 0.87 mm,The cumulative surface settlement is mainly distributed in the range of 5～20 mm,with an average value of 9.61 mm.At the same time,the monitoring results also verify the applicability of the proposed theoretical method（the stability discrimination method of mining overburden structure under building load）.The above research puts forward a theoretical method for the stability evaluation of goaf under building load,establishes the mechanical model of mining overburden structure under load,and gives the criterion formula of mining overburden structure stability under building load,which provides a new idea for the foundation stability evaluation of new buildings in subsidence area,and applies this method to practical engineering,the feasibility of the method is verified.