Study On The Influence Mechanism Of Floor With Different Sedimentary Combination Structure On Mining Effect In Huaibei Coalfield

Based on the analysis of geological data of Huaibei coalfield,this paper divides the floor sediment assemblage structure of main coal seam,and studies the influence mechanism of floor with different sediment structure on mining effect by means of laboratory similar material test,numerical simulation and floor strain monitoring.The main conclusions are as follows:(1)Through collecting and analyzing the hydrogeological data of Huaibei coalfield,it is concluded that the main structure of the main coal seam floor in Huaibei coalfield can be divided into two categories:intact floor and incomplete floor.The sedimentary assemblage structure of intact floor includes four sub-categories:soft-hard-soft floor,interbedded floor,hard-soft floor,hard-soft-hard floor,and non-intact floor including two sub-categories:concealed fault floor and concealed subsidence column floor.There are two categories,six sub-categories of floor model.(2)Through the similar material simulation test,the failure law,displacement change law and the transfer law of mining stress in horizontal and vertical directions of the interbedded floor during excavation are studied in depth.It is found that during the excavation of similar material model,the mining stress concentrates in the mudstone at the depth of 25cm of the interbedded floor,which prevents the mining stress from transferring to the deep strata.This indicates that the mudstone(soft rock)has an "adsorption" effect on the stress in the interbedded floor and produces a stress buffer effect on the hard strata above.(3)By using FLAC3D numerical simulation software,plastic zone development characteristics,the stress distribution characteristics and floor displacement variation characteristics of two and six kinds of floor models established in the course of coal seam advancing are studied in depth.It is concluded that the direct bottom hard rock layer in the complete floor acts as a "rigid beam" and restrains the deformation of underlying rock layer,while the soft rock layer acts as a "mattress" for the upper rock layer.The cushion effect blocked the transmission of mining stress to the deep part,but in the non-complete floor(including hidden faults and subsidence columns),the hidden defective structure would cause the uneven distribution of floor stress,aggravate the damage of the floor near the concealed structure,increase the damage depth and scope of the floor,weaken the thickness of the effective water-proof layer of the floor,and increase the threat of water inrush from the floor.(4)The bottom plate strain monitoring system is used to monitor the damage depth of the bottom plate of the ?633 working face.By analyzing the micro-strain of the bottom plate at different depths of the bottom plate,the damage depth of the bottom plate after grouting reinforcement is obtained,and the measured strain data and the working surface are obtained.The characteristic parameters of the mine pressure are compared and analyzed to explore the intrinsic relationship between the two.In addition,the accuracy of the on-site strain monitoring is obtained by comparing the theoretical calculation of the damage depth of the bottom plate and the difference of the numerical simulation results before and after grouting.