Research On The Foundation Stability Of The Overlying Bridge In The Mined-out Area

China is abundant in coal mines resources,however,with the massive exploitation of coal mines,water and environment are polluted and destroyed,and the destruction of surface structures caused by mining subsidence,and it is believed that the mining subsidence causes the most serious consequences.With the development of China's infrastructure construction,a large number of goafs will be used as construction sites.Research on subsidence and foundation stability of construction structures has been inevitable.However,the traditional theoretical research methods are single and its research results differ greatly from the actual situations,so it is necessary to adopt more efficient and reliable method in research and to guide the engineering practice.This paper taking Dahebian Highway Bridge in Dahe Town,Zhongshan District,Liupanshui City,Guizhou Province as example obtains the information of geology,mining and rock mechanics parameters by means of on-site geological survey and data collection.On this basis,it uses the random medium theory to calculate the surface deformation of the macro-Longzhai coal mine goaf,and then establishes a three-dimensional model of the goaf by software(MIDASGTSNX).By comparing and analyzing the theoretical calculation and numerical simulation results,it analyzes the stability of the site of goaf and determines the site selection of bridge pier foundation based on the field monitoring data and relevant specifications.The main achievements of this subject are as follows:(1)On the basis of absorbing the research results of predecessors in the field of mining subsidence,the advantages and disadvantages of current research on mining subsidence theory at home and abroad are comprehensively analyzed,and the deformation and failure characteristics of overlying strata in goaf are discussed in this paper.(2)The different expressions of stochastic medium theory under the conditions of full and insufficient exploitation of coal seam with different inclination are introduced,and the methods to obtain the calculation parameters are discussed in this paper.(3)The settlement,horizontal movement,inclination,curvature and horizontal deformation of the main section and the main section heading toward the main section are calculated by the stochastic medium theory formula.The software simulates the settlement,horizontal movement and stress of overlying strata and surface in the goaf.According to the theoretical calculation and simulation results,the current collapse state of the goaf and the grade of damage to the building are confirmed.(4)Combined with the time of mined-out,the monitoring results of surface movement and deformation,the roof lithology and the coal mining depth-thickness ratio,the current goaf is in a stable state generally.Under the influence of groundwater,blasting,earthquakes and the upper load,the mined-out area may collapse and be destroyed.It is suggested that the foundation of the pier should be selected outside the affected area of the goaf.(5)By calculating the influence radius of goaf along the trend,the site selection of bridge pier foundation is determined.The influence of bridge load on the overlying strata in the goaf and the selected foundation of the bridge piers is simulated by theoretical calculation and software,and the reliability of the site selection is verified as well.