Research On The Support Technology Of Composite Roof Retraction Passage With Ooze Invasion In Multi-hole Karst Area

The roof of Yongju Coal Industry 10#coal seam is hard limestone,there are a lot of holes in the roof rock layer,and there is local invasion of soft mud.During the withdrawal of the coal mining face,there are several roofing and frame accidents during the withdrawal channel,resulting in great economy Loss and potential safety hazards,the support of Yongju Coal Industry 10#coal seam large section withdrawal channel has no experience to learn from in other mining areas,in order to avoid accidents such as pressing frame and roof leakage during the removal of working face equipment Affecting mine safety production requires systematic research on this issue.This paper takes the large section withdrawing channel of Yongju Coal Industry 10#coal seam fully mechanized coal mining face as the engineering background,and systematically studies the conditions of porous roof composite roof through field investigation,theoretical analysis,numerical calculation,numerical simulation and field engineering practice.The deformation and failure law of the large-section withdrawal channel reveals the mechanism of instability and deformation of the surrounding rock.Based on this,the support concept with the integrity and integrity of the roof as the core is proposed.1.The surrounding rock control technology dominated by a single column+?-shaped beam has mainly achieved the following results:The typical failure characteristics of the surrounding rock of the porous tunnel composite roof withdrawal channel are:the rock surface of the roof is hard and the cracks are broken,frequent roofing accidents,large-scale roof roofing or cutting collapse along the coal stile cause a frame accident;It is soft and broken,and the pieces are obvious.Peeping through the roof drilling shows that:within 0?4m of the roof rock layer,fissures are developed and there are slight separations;within 4?8m of the roof rock layer,karst caves are developed,and there are a large number of holes.The joints and cracks of the rock body are fully developed,the strength is low,and the fracture is loose;The top rock layer of 8m and above,the rock mass is hard and complete.The rock quality index(RQD value)within 4?8 m of the roof rock layer of Yongju Coal Industry 10#coal seam is about one-third of the rock layer with a depth of more than 8 m,about one-half of the rock layer with a depth of 0?4 m The compressive strength and tensile strength of the rock are obviously lower than those of the rock samples in the range of 0?4 m and 8?13 m.The development of holes leads to a significant reduction in the integrity,continuity and integrity of the rock mass.The roof cantilever beam length of Yongju coal industry 10#coal seam withdrawal channel is 11.3 m,the depth of unstable rock layer of the roof is less than 12 m,and the object supported by the roof of the withdrawal channel is the basic roof of limestone with an average thickness of 12.79 m.There are many holes and groups of structural planes in the hole development area of limestone,which greatly reduces the strength,self-stability and bearing capacity of the rock mass in this area.It is preliminarily proposed that the surrounding rock instability mechanism of the roof withdrawal channel in the development of the hole:after the withdrawal channel is excavated,the cracks in the shallow rock layer of the roof extend and the joints and cracks expand in the hole development area,which further increases the depth of the unstable rock layer of the roof.Integrity and integrity are continually decreasing,and the rock formation in the hole development area is prone to large separation,which gradually develops into roof fall or large-scale fall-off collapse,resulting in a crash accident.The FLAC^3Dnumerical simulation software was used to simulate and analyze the effect of the development of holes on the stability of the surrounding rocks of the withdrawal channel.The results show that the shallower the development layer of the roof hole,the greater the impact on the stability of the surrounding rock of the roadway;Moving towards each other,the surrounding rock of the cavity is obviously damaged by shear;the greater the distribution density of the cavity,the more severe the plastic failure of the roof and the greater the surface displacement.When the volume of the cavity reaches 25%of the entire cavity development area,the roof will fall along the coal wall The collapse of the surrounding rock and the overall instability of the surrounding rock of the withdrawal channel fully indicate that the development of holes is a key factor that makes the surrounding rock of the withdrawal channel difficult to control,and the failure mechanism of the roof of the withdrawal channel is verified.According to the destruction characteristics of the porous roof composite roof,the roof rock layer is divided into fracture fracture area,hole development area,and hard self-stability area,and a multi-level support technology with the guarantee of roof integrity and integrity as the core is proposed to analyze the permanent polymerization The problems existing in the existing support of the coal industry withdrawal channel,combined with specific engineering examples,design a multi-layer surrounding rock control technology plan dominated by high-strength prestressed anchor rods,hollow grouting anchor cables,single columns+?beams,Analyze and discuss the influence of the prestress and length of the anchor rod and cable on the support effect,and select the appropriate support theory to determine the specific parameters of the anchor rod and cable support.Field investigation and mine pressure monitoring during the field application showed that the new scheme fully mobilized the bearing capacity of deep stable rock layers,and the deep rock layer and shallow rock layer were combined into a stable bearing structure,giving full play to the self-supporting and bearing capacity of the surrounding rock and effectively controlling The separation,relative movement and crack expansion of the roof rock layer are developed,and the amount of roadway roof subsidence is controlled within a reasonable range,which prevents the discontinuous large deformation of the roof and the occurrence of roof fall,and has achieved good application results.The research results have important practical significance and far-reaching historical significance.