Analysis Of Subgrade Activation And Dynamic Response Characteristics Of Goaf Under Dynamic Load Of Taijiao High Speed Railway

China is rich in coal resources,but as a large amount of coal is mined every year,it also leaves a lot of goafs.On the other hand,with the continuous encryption of the railway construction network,some railway construction will inevitably pass through the coal mine goaf.If a high-speed railway is built above the mined-out area,the dynamic load caused by the train may cause the mined-out area to reach a new state of settlement and cause the“activated”deformation and settlement of the mined-out area again.This paper relies on the existence of the goaf in the DK259+135.95-DK259+710.00 line section of the Taijiao（Taiyuan-Jiaozuo）high-speed railway as the engineering background,and combines the fuzzy comprehensive evaluation method and FLAC^3D numerical simulation software for the goaf foundation under the dynamic load of the high-speed railway.The research on the dynamic characteristics of the roadbed and the judgment of"activation"are conducted.The main conclusions are as follows:（1）In view of the characteristics of many factors affecting the“activation”of the goaf,the method of fuzzy comprehensive evaluation and establishment of the“activation”grade table is selected.The"activation"grades of the mined-out area before and after the applied dynamic load are evaluated and compared with the actual project to verify the feasibility of the fuzzy comprehensive evaluation method.（2）The numerical simulation study shows that the response of the roadbed above the mined-out area is the largest at the surface of the bed under the dynamic load of the train,but it decreases with the increase of the roadbed depth.Among them,the main attenuation part of dynamic stress and dynamic displacement mainly occurs at the base layer of the road;the main attenuation part of vibration velocity and vibration acceleration is mainly at the surface layer of the roadbed.（3）After the mining ground is subjected to the dynamic load of the train,when the mining depth is the same,the maximum settlement of the surface is proportional to the speed of the train;at different mining depths,the deeper the mining depth,the less the effect of the mining area on the ground,The lower the probability of causing"activation"of the goaf.（4）Under different working conditions,the location and state of the plastic zone of the goaf will change accordingly.Tensile failure mainly occurs near the roof of the goaf,and shear failure occurs on both sides of the goaf.Under the same geological conditions,the volume of the plastic zone increases with the volume of the goaf.