The Study On The Strata Movement And Mine Pressure Behavior Under The Extra-thick Coal Seam Mining Based On The Physical Model And Discontinuous Deformation Analysis

Coal is the main source of energy in China.In 2019,it accounts for about 58% of China's disposable energy consumption structure,and it is expected that it will still account for more than 40% by 2050.Extra thick coal seam is the main seam for productive and efficient mining of coal mines in China.In order to clarify the movement disturbance under the extra thick coal seam mining and mine pressure regularity.In this paper,by means of laboratory testing,physical simulation and numerical simulation,the characteristics of overburden deformation and fracture movement are deeply analyzed,and the characteristics of overburden fracture and instability are revealed,and the influence law of rock strata movement on mine pressure behavior is obtained.The main results are as follows:(1)The basic mechanical properties and failure characteristics of overburden in situ are studied.The TAW-2000 microcomputer servo rock triaxial shear testing machine system was used to carry out conventional compression and acoustic emission tests on the field rock samples.Under the condition of uniaxial compression,the rock samples showed strong brittle failure characteristics.With the increase of confining pressure,the elastic modulus,compressive strength,axial deformation and acoustic emission ring count of rock samples increase gradually.(2)Fracture characteristics and motion law of hard roof in extra thick coal seam mining.Under the mining condition of extra thick coal seam,the structure of "simply supported beam" is formed because the bearing capacity of roof is better and the layer separation is obvious.With the mining depth increasing,the roof subsidence displacement above the goaf of coal seam working face increases gradually with the increase of goaf.At the initial stage of working face mining,fine cracks appeared in the roof above the goaf.When mining 195 m,a short "cantilever beam" structure is formed after the immediate roof is broken.As the mining continues to advance,the upper roof periodic fracture occurs when mining 270 m.At this time,the structure presents an arched bridge structure,and the key stratum separation phenomenon occurs.When mining at 292.5m,the inferior key stratum begin to break and collapse,and each rock block is extruded and occluded,forming a multi-cantilever structure.When mining at315 m,the key stratum was broken,the roof above the goaf completely collapsed,and the whole structure collapsed and became unstable.(3)The breaking instability conditions of overburden key stratum in exploitation of extra thick coal seam.Under the disturbance of extra-thick coal seam mining,the overburden fracture movement experienced two gentle phases and two surge phases in fractal dimension.In the gentle phase I,the main manifestation is the initiation and extension of direct roof crack.The surge phase I mainly occurs in the destruction process of the immediate roof.The gentle phase II occurred in the stage of secondary collapse of the upper roof and the inferior key stratum subsidence.The surge stage II occurred in the early stage of the key stratum breakage.It can be seen that the processes of overburden movement are immediate roof fracture,upper roof fracture and key stratum fracture.The periodic fracture of upper roof and subsidence fracture of inferior key stratum have relatively weak influence on the overall overburden movement.So it can be inferred that the second surge of the fractal dimension of overburden topography is the condition of the far-field inferior key stratum fracture.(4)The influence law of overburden key stratum movement on the mine pressure behavior in the mining of extra thick coal seam.With working face advancing,the principal stress on the far-field key stratum gradually evolved into horizontal direction,and increases first and then decreases with the advance of working face.The reason is the masonry beam structure formed by the block after the key layer is broken,and the broken blocks squeeze and bite each other,resulting in the change of stress direction and magnitude.At the same time,the internal stress decreases with the full relative movement of the fracture block in the key layer.At the initial stage of mining,the stress in front of the working face increases gently.At this time,there is no fracture in the farfield key stratum,and the bearing capacity of each part of the key stratum is strong,so the stress accumulation process in front of the working face is relatively slow.With the gradual increase of mining distance,the key stratum fracture occurs.Because the interlocking masonry beam structure formed by the broken key layer block is stable,the pressure conduction effect is obvious,leading to the increasing pressure in front of the working face.(5)Study on the breaking law of overburden roof under the influence of fault.The simulation results show that the stress concentration occurs at the working face of the extra thick coal seam with fault,which is consistent with that without fault.In addition,the stress concentration also occurs at the fault position.With the advance of the working face,the failure range of the roof increases,and the rock strata close to the fault are damaged on account of weak stress intensity.The stress on the overburden roof increases with the advance of the working face.When the inferior key stratum are fully broken and subsided,the relative movement of the broken block is more sufficient,and the stress on the key stratum decreases.Under the influence of fault,overburden stress is redistributed sharply,leading to the formation of "arch" supporting structure of key stratum and its underlying strata.Therefore,the fracture range is weakened during caving,and the subsidence displacement of key stratum before rupture is smaller in the presence of fault than in the absence of fault.The maximum displacement of the key stratum in the presence of fault is greater than that in the absence of fault.In the presence of fault,the stress release at the fault layer is larger,and the stress in the key stratum is higher than that in the absence of fault.This paper has 53 figures,9 tables and 82 references.