| The return airway of 1307 working face of Sweetwater Fort Coal Mine is a triple soft coal seam roadway.Although it can achieve good support effect at the initial stage of support,the rheology of soft rocks and its own capacity expansion make the roadway very prone to loose and broken surrounding rocks,anchor structure failure and mud disintegration again.In this thesis,a systematic study on the deformation mechanism and reinforcement technology of three soft coal seam retrieval roadways is conducted,and the main research results achieved are as follows:(1)The physical and mechanical properties of typical coal rock bodies were mastered.The mineral composition and microstructure of the top and bottom slabs were measured and analysed,and the average percentages of clay minerals in the top slab mudstone and bottom sandy mudstone were 32.05% and 34.4% respectively,and the pore and fissure spaces were developed;the compressive strengths of the 3# coal and top and bottom slab rock samples were determined to be 7.26 MPa,11.71 MPa and 14.59 MPa respectively,and the tensile strengths were 0.392 MPa,0.947 MPa and 1.438 MPa respectively.The tensile strengths were 0.392 MPa,0.947 MPa and1.438 MPa respectively,which were typical of three soft coal seams;the maximum damage range of the top,high side and low side of the roadway was 5.1m,4.14 m and3.82 m respectively,and the overall deformation rate of the section was as high as 38%,and the surface deformation showed the characteristics of "high side > low side >bottom plate > top plate".(2)The deformation mechanism of the surrounding rock was analysed.The deformation of the top slab is identified as a delaminated damage type,the deformation of both sides is a composite type of shear-slip type and splitting type,and the deformation of the bottom slab is a composite type of extruded flow type and water swelling type of bottom drum.The failure mechanism of the support structure is that the loose circle of the surrounding rock expands beyond the anchorage range of the joint support,resulting in the loss of bearing capacity of the support structure of the roadway.The core of reinforcement is to promote the formation and strengthening of the overall bearing structure of the surrounding rock,thus proposing the joint reinforcement idea of "strong side reinforcement and bottom drum control" by combining high preload anchor cables with full-length anchor reinforcement anchors.(3)A combination of orthogonal tests and numerical simulations was used to establish the L9(3×4)orthogonal scheme table with four factors and three levels of anchor anchor length,anchor cable length,anchor cable density and anchor cable preload.The effect of reinforcement under each scheme was studied,and the sensitivity of each factor was clarified by using the extreme difference analysis method.The bottom slab is reinforced with two Φ20×2400 mm anchor rods at 25°from the vertical direction(to the outside)at a distance of 0.2 m from the roadside,with a spacing of 800 mm;the anchor rods are reinforced with full-length anchors to strengthen the bond.(4)Industrial tests were carried out on site.The surface displacement monitoring showed that the maximum displacement of the top and bottom slab was 154 mm,and the maximum displacement of both sides was 156 mm.The average displacement of the top and bottom slab was reduced by 84.5%,and the average displacement of both sides was reduced by 87.5%.The monitoring of the anchor rod and cable preload showed that the maximum anchor force of the top plate was 121 k N and 209 k N,and the maximum anchor force of the anchor rod and cable on both sides was 114 k N and197 k N respectively,which were within the reasonable range.There are 66 pictures,17 tables and 100 references in this thesis. |
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