Research On The Damage Mechanism And Control Technology Of Centralized Tunnel Bottom Drum Under Repeated Mining Of Multiple Coal Seams

Repeated mining of multiple coal seams leads to serious deformation of the surrounding rocks of the coal seam bottom rock concentration alley,which seriously affects the realization of the functions of coal transportation,material transportation,pedestrian and ventilation of the concentration transport alley,track alley and return air alley,and causes unfavorable ventilation due to the contraction of the alley section,and the alley needs repeated maintenance,which seriously affects mine safety and efficient production.In this paper,the +400m level transport roadway,track roadway and return air roadway of a mine are the objects of study.After this group of roadway is affected by the dynamic pressure of No.2 coal seam and No.4 coal seam,it is also affected by the repetitive mining of No.5 coal seam,the main characteristics of the damage of the surrounding rock of transport roadway,track roadway and return air roadway are rapid deformation of roadway,serious bottom drum,two gang pressure crisp,etc.Through theoretical analysis and numerical simulation,we study the mechanism of bottom drum deformation of track roadway under repeated mining of multiple coal seams.Through theoretical analysis and numerical simulation,we study the deformation mechanism and law of the bottom drum in the railroad tunnel under repeated mining,and propose the control technology of the bottom plate of the tunnel,which can provide theoretical guidance for the control of the bottom drum of the centralized tunnel in the mine.The main results of this paper are as follows:(1)The arrangement condition of centralized tunnel and its support conditions,coal seam structure,ground stress field distribution and rock mechanics parameters were clarified through on-site research.(2)Systematically analyzed the main factors of the bottom drum of the centralized railroad tunnel,established a mechanical analysis model of the bottom drum of the tunnel,and obtained the stress equation of the bottom slab surrounding rock that leads to the bottom drum of the tunnel,and also established a stress transfer mechanical model of multi-seam mining,which can analyze the stress component at any point of the coal seam bottom after the nth coal seam mining.(3)With the help of FLAC3D numerical simulation software,a numerical simulation model for analyzing the floor heave of a multi seam mining floor concentrated roadway is established.Under the initial support conditions of the concentrated roadway,the mining of coal seams 2,3+4,and 5 is sequentially simulated.The stress distribution characteristics,displacement and deformation laws of the surrounding rock,and the distribution of plastic failure zones of the concentrated track roadway are analyzed.Research has found that the mining of coal seam 2 has a relatively small impact on the deformation and damage of the surrounding rock of the main roadway.Compared to the excavation of larger tunnels,the amount of floor heave only increases by about 2 mm,and the amount of roof subsidence increases by about 5 mm.The mining of the 3+4 and 5 coal seams has a significant impact on the stability of the surrounding rock of the main roadway.The deformation of the surrounding rock of the main roadway is mainly reflected in the sharp increase in the amount of floor heave.After the mining of the 3+4 coal seam,the amount of floor heave in the main roadway is 448.00 mm.Due to the influence of the mining of the 5 coal seam,the amount of floor heave in the main roadway reaches 556.78 mm.(4)Three kinds of control schemes for the bottom slab of multi-seam mining are proposed,namely bottom anchor support,bottom slab slotting and pressure relief,and concrete anti-bottom arch support,and the parameters of the three control schemes are optimized by using theoretical analysis and numerical simulation.Numerical simulations were conducted to study the deformation and damage of the surrounding rocks of the multi-seam repetitive mining tunnel under the three support schemes,which showed that: under the condition of anchor rod support in the bottom plate,the bottom drum volume of the tunnel was 482.11 mm after mining the No.5 coal seam,which failed to form an effective control of the bottom drum of the tunnel;the support measures of slotting and pressure relief in the bottom plate and concrete anti-bottom arch could effectively control the bottom drum deformation of the tunnel.After the No.5 coal seam was mined,the bottom drums of the two options were 113.75 mm and 101.04 mm respectively,and the support option of slotting and unloading of the bottom slab was more suitable as a means of controlling the bottom slab.(5)The bottom drum section of the centralized tunnel was selected for field test research,and the bottom drum control was carried out by using the support scheme of slotting and pressure relief and concrete anti-bottom arch support scheme respectively,and the field monitoring data showed that the bottom drum control scheme of excavating a slot width of 800 mm and a slot depth of 2000 mm on both sides of the tunnel bottom and backfilling with gangue was optimal.Under this control scheme,the bottom drum volume of the alley is stabilized at156 mm,and the bottom drum of the alley is effectively controlled.