Research On Mechanical Properties And Control Technology Of Grouted Surrounding Rock Of Large Section Roadway With Soft And Weak Coal Sides

The support of surrounding rock of large section roadway with soft and weak coal sides under the complicated conditions were difficult yet significant. Funded by National Natural Science Foundation Project “Rapid excavation and support of large section roadway” and Outstanding Innovative Talents Foundation Project of Doctoral Students of CUMTB “Laboratory grouting test of soft and weak coal rock”, the paper studied the mechanical properties and control technology of grouted surrounding rock of large section roadway with soft and weak coal sides based on laboratory test, numerical simulation, theoretical analysis and field test,which the research background was the support of No.2 mining area rail roadway with soft and weak coal sides in Shuguang Mine. The main research results were as follows. Geomechanics evaluation and research on supporting measures of No.2 mining area large section roadway with soft and weak coal sides in Shuguang MineLaboratory test results showed that the coal seam on the rail roadway sides in No.2 mining area in Shuguang Mine was soft and weak. The strength of mudstone on the roof and floor was low and rich in clay minerals, such as mixed-layer of illite and montmorillonite, illite, kaolinite. The surrounding rock on the roof and floor belonged to strong expansive soft rock.In-situ stress test results showed that in-situ stress field in No.2 mining area in Shuguang Mine was dominated by gravity stress. The angle between the maximum principal stress and vertical plane was 5°. It was close to vertical. The maximum principal stress was 14.35 MPa. The angle between the intermediate principal stress and horizontal plane was 2.84°. The intermediate principal stress was 12.80 MPa. The angle between the minimum principal stress and horizontal plane was 4°. The minimum principal stress was 8.92 MPa. The direction of the intermediate principal stress and the minimum principal was mostly perpendicular to the maximum principal stress.The test results of loose circle of surrounding rock in acoustic method and peering method showed that the loose circle range on the roof and sides of No.2 mining area roadway in Shuguang Mine was 2.0-2.2m and 2.3-2.8m. It belonged to typical large loose circle. The whole 2# coal seam on the roadway sides was relatively broken.The No.2 mining area rail roadway in Shuguang Mine belonged to large section roadway with soft and weak coal sides based on engineering situation, surrounding rock physical and mechanical characteristics, surrounding rock mineral composition contents, the magnitude of roadway in-situ stress, surrounding rock loose circle range. In addition, the paper analyzed the mechanism of deformation and failure, reinforced support principle of surrounding rock, proposed the combined support of anchor cable and grouting with deep and shallow holes of large section roadway with soft and weak coal sides. Research on laboratory grouting test and micro-mesoscopic characteristics of surrounding rock of large section roadway with soft and weak coal sidesThrough testing syneresis rate and induration’s uniaxial compressive strength of 18 kinds of PO42.5 ordinary portland cement grout and 36 kinds of superfine cement grout which specific surface area was 800m2/g with different water cement ratio and bentonite proportion, the results showed that superfine cement grout with water cement ratio 1: 0.6 and bentonite in 4% of cement weight which the syneresis rate was 6% and uniaxial compressive strength after curing 28 d was 8.87 MPa met the requirements of laboratory grouting to equivalent specimens of coal seam destructed.The specimens which the diameter was 0-55 mm, the height was 0-200 mm could be grouted in laboratory by the self-developed MYZJ-2 hydraulic pressure grouting system. The range of grouting pressure was 0-6MPa. It could realize to grout standard specimens in different grouting pressure and related research.The test results of grouting specimens in laboratory by self-developed hydraulic pressure grouting system with optimized grout ratio showed that depending on consolidation of grout to multiple cross fracture of specimens, the strength of specimens increased and in the range of 0-2MPa, the peak strength and post-peak residual strength of grouted specimens increased continuously with the increasing of grouting pressure. When the grouting pressure was 0.5MPa, 1.0MPa, 1.5MPa, 2.0MPa, the post-peak residual strength of grouted specimens increased 23.8%, 50%, 60.9%, 73.9% compared to the specimens before grouting. The material properties of grouted specimens was transformed from linear elastic into elastic-plastic at first and then into nearly perfectly plastic. And the bearing capacity of grouted specimens increased. The grouting effect was good.The test results of CT scanning, calculation of fracture fractal dimension, SEM electron microscope scanning of equivalent specimens of coal seam destructed before and after grouting showed that after the compressed destruction of intact specimen of coal seam, there were a lot of mesoscopic fractures inside the specimens and the fracture morphology had the characteristics of obvious river-like brittle fracture. After grouting the specimens, the fracture was substantially filled with grout and the integrity of specimens was restored. In the range of 0-2MPa, the fracture fractal dimension of grouted specimens decreased continuously with the increasing of grouting pressure. When the grouting pressure was 0.5MPa, 1.0MPa, 1.5MPa, 2.0MPa, the fracture fractal dimension of grouted specimens decreased 19.27%, 18.05%, 23.58%, 24.16% compared to the specimens before grouting. After the compressed destruction of grouted specimens, the surface of fracture was substantially covered with superfine cement and the particles of coal were cemented together with each other. The fracture morphology had not the characteristics of obvious brittle fracture. It changed the characteristic of brittle failure of the specimens of coal seam.It had certain bond force between grout and fracture surface of equivalent specimens of coal seam destructed after grouting. After the compressed destruction of grouted specimens, the failure zone of specimens mainly was grouting reinforced zone. The rupture mechanism of specimens did not change. Research on numerical simulation of stability of grouted surrounding rock of large section roadway with soft and weak coal sidesDeformation of surrounding rock in the original supporting scheme of No.2 mining area rail roadway in Shuguang Mine was larger. Plastic tensile failure appeared in the shallow surrounding rock on the floor of roadway. Plastic shear failure appeared in the shallow surrounding rock and deep surrounding rock on the sides of roadway. The stress of shotcrete layer and anchors exceeded the ultimate bearing range. The supporting strength of surrounding rock was serious shortage.The deformation of surrounding rock was controlled significantly after grouting the surrounding rock in the range of loose circle. The reinforcement effect of grouting surrounding rock of the whole roadway section was better than grouting on the sides or roof. Among them, there was small difference of the reinforcement effect between grouting surrounding rock of the whole roadway and on the sides. Because the broken coal on the roadway sides was the weakest surrounding rock, grouting on the sides could restore the integrity of coal, improve the bearing capacity of coal, support the load of roadway roof, control the deformation of roadway roof and floor. Under the premise of ensuring safety, the method of grouting surrounding rock on the roadway sides would be used to support the surrounding rock in the range of loose circle.On the basis of grouting shallow broken surrounding rock on the sides of roadway, grouting and using the anchor cables to support the different depth of plastic failure surrounding rock on the deep sides could further control the deformation of surrounding rock. In the range of 2-10 m of grouting depth, the deformation of surrounding rock showed a trend of decreasing at first and then increasing with the increasing of grouting depth. When the grouting depth was 4-6m, the deformation of surrounding rock could be controlled in the maximal degree. In addition, In the range of 2-10 m of grouting depth, it obtained the relation between grouting depth and deformation of the roadway sides, deformation of the roof.When the deep coal in the range of plastic zone was grouted, the anchor cables could obtain the pull point in the coal, full play the tensile effect. It could also decrease the deformation of surrounding rock.Based on research results of numerical simulation and supporting measures of large section roadway with soft and weak coal sides, the paper proposed the combined support of anchor cable and grouting with deep and shallow holes of No.2 mining area rail roadway in Shuguang Mine. The deformation of the roadway sides, roof, floor decreased 70.5%, 40.2%, 24.5% compared to the surrounding rock supported in the original scheme when the surrounding rock was grouted and reinforced by anchor cable in two sides. The maximum thickness of plastic zone of the roadway sides, roof, floor was 2.50 m, 0.88 m, 2.21 m. The stress of shotcrete layer and anchors did not exceed the ultimate bearing range. The deformation of surrounding rock was controlled. The deformation of the roadway sides, roof, floor decreased 41.3%, 14.3%, 13.3% compared to the surrounding rock supported in the original scheme when the surrounding rock was grouted in right side and reinforced by anchor cable in two sides. The maximum thickness of plastic zone of the roadway left side, right side, roof, floor was 3.88 m, 2.60 m, 1.32 m, 2.65 m. The stress of shotcrete layer and anchors exceeded the ultimate bearing range. The anchor cable may be broken by tension or shear. The deformation of surrounding rock on the left side was not controlled. Research on mechanical properties of grouted structural body of large section roadway with soft and weak coal sidesResearch results of the stress-strain curves and failure process of anchor, anchor cable, surrounding rock of roadway with soft and weak coal sides before and after grouting showed that the constitutive model of A3 steel anchor and surrounding rock of roadway with soft and weak coal sides before and after grouting was St.Venant body which was composed by elastic element and plastic element in series. It was an ideal elastic-plastic body. The constitutive model of l-prestressed strand anchor cable was Hooke body which was composed by an elastic element. It was an ideal elastic body.Through the analysis on four stress-strain processes under the shear load to anchor in the roadway sides and surrounding rock of roadway with soft and weak coal sides after the excavation of roadway, the constitutive model and equation of surrouding rock of roadway with soft and weak coal sides in the range of loose circle and supporting system were obtained.Through the analysis on reinforced support action of grouting of the shallow coal in the range of loose circle and the deep coal in the range of plastic failure zone, anew constructed anchors in the coal seam which were broken or invalid in the original supporting scheme, anchor cables in the coal seam, the stress-strain processe under the shear load to anchor, anchor cable in the roadway sides and grouted surrounding rock of roadway with soft and weak coal sides could be divided into two sections. In addition, the constitutive model and equation of grouted surrouding rock of roadway with soft and weak coal sides and supporting system were obtained. Research on field application of grouting reinforcement technique of large section roadway with soft and weak coal sidesBased on the above research, the No.2 mining area rail roadway in Shuguang Mine used two grouting supporting forms to reinforce the surrouding rock which were grouted in right side and reinforced by anchor cable in two sides, grouted and reinforced by anchor cable in two sides. The results of ground pressure monitoring showed that the deformation of grouted surrounding rock was controlled significantly. When the surrounding rock was grouted and reinforced by anchor cable in two sides, the deformation of the roadway sides, roof and floor decreased about 50%, 30% compared to the surrounding rock which was grouted in one side, decreased about 85%, 80% compared to the surrounding rock supported in the original scheme. The roadway roof bed separation volume of grouting in two sides decreased about 60% compared to the surrounding rock grouted in one side.The results of loose circle range test of surrounding rock in acoustic method and peering method showed that the loose circle range on the left side, right side, roof of roadway surrounding rock was 2.5-2.7m, 1.5-1.7m, 1.1-1.3m when the surrounding rock was grouted in right side and reinforced by anchor cable in two sides. The loose circle range on the left side, right side, roof of roadway surrounding rock was 1.5-1.7m, 1.3-1.5m, 0.6-0.8m when the surrounding rock was grouted and reinforced by anchor cable in two sides.Grouting reinforcement of surrounding rock on soft and weak coal sides restored the integrity of broken coal, decreased the loose circle range of surrounding rock, increased the bearing capacity of coal, improved the stress condition of coal, decreased the bearing pressure of the roadway roof, could save the cost of grouting reinforcement compared to grouting surrounding rock of the whole roadway, accelerated the construction speed. The combined support of anchor cable and grouting with deep and shallow holes could close the shallow surrounding rock of roadway, prevent the leakage of grout, let the anchor cables obtain the pull point in the coal, effective control the deformation and roof bed separation volume of surrounding rock, ensure the stability of surrounding rock.