| Based on laboratory experiment, numerical simulation, theoretical analysis and filed test, we have carried out some research on the effectiveness and filed practice of grouting-reinforcement in deep roadway of Jiulong Coal Mine. The results proved that:(1) Using hollow inclusion technique expressed that the horizontal tectonic stress is the main stress of geostress field at-850 m level in Jiulong Coal Mine, the maximum principal stress made an average angle of 235.7 with horizontal plane, the minimum principal stress made an average angle of 49.8 with horizontal plane; the another principal stress made an average angle of 136.3 with horizontal plane, maximum principal stress is about 23.4MPa, intermediate principal stress is about 18.1MPa, minimum principal stress is about 16.1MPa. The maximum principal stress made a lager angle with main roadway at-850 m level in Jiulong Coal Mine; it is not good for stability and maintenance of roadway. The side and immediate floor of main roadway are made up of mudstone at-850 m level, main mineral components were quartz, iron pyrite, siderite and clay mineral whose ratio was more than 50%, main contents of clay mineral were illite / montmorillonite, illite and kaolinite; in mineral composition, the percentage of illite / montmorillonite mixedlayer is up to 69% and the percentage of kaolinite is 21%, it is a kind of strong expansive soft rock roadways, the property of side wall-rock would become worse after excavation. The wall-rock of hard roof and hard floor was siltstone at-850 m level, lithology of wall-rock was well and its strength is greater than 50 Mpa, the wall-rock of immediate roof and side was sandy mudstone, and its strength was lower than 40 Mpa, the wall-rock of immediate floor whose strength was lower than 10 Mpa was Wild blue limestone, internal friction angle and cohesive force were both small, roadway was easily destroyed.(2)After excavation of main roadway at-850 m level in Jiulong Coal Mine, due to cover depth of roadway and influences of deep high earth pressure, the wall-rock of roadway was broken, the deformation became lager, especially the wall-rock of two sides, partial deformation was larger than 1m, it brought great hidden danger to safety production of coal mine, high earth temperature, high karst water pressure and strong mining disturbance, the range of roof wall-rock broken zone was up to 0.8m-1.5m of main roadway at-850 m level in Jiulong Coal Mine, the range of right side broken zone was up to 1.4m-1.8m and the range of left side broken zone was up to 1.4-2.0m, it is belong to range of large broken zone. With forward excavation, wall-rock cracks got different levels of development and its rate was rapid in the same gaging hole, deformation of roadway rock-wall was serious as a whole. During excavation and timbering, it is necessary to enhance timbering of roadway. To guarantee driving speed and normal use of main roadway at-850 m level in Jiulong Coal Mine, we expected to apply “flexibility first, stiffness second” grouting-reinforcement technique to reduce strength of first reinforcement properly and control wall-rock deformation.(3)By means of CT scanning experiment and fractal dimension calculation of cracks, it showed that grout filled cracks of destroyed specimens after grouting, the wholeness of specimens recovered; fractal dimension of cracks was about 1.4 before grouting while 1.0 after grouting, later fractal dimension was obvious less than previous one, it verified that the effectiveness of grouting specimens was great in microcosm. Adopting superfine cement grout that whose water-cement ratio was 1:0.6 and bentonite was 4% of cement, longitudinal strain and transverse strain of destroyed specimens after grouting were obvious bigger than the ones before grouting, the curve of whole mudstone uniaxial compressive strength stress-strain was almost linear, toughness of specimens was bad, brittle facture easily occurred, while the curve of whole mudstone uniaxial compressive strength stress-strain was nonlinear after grouting, laboratory experiment of grouting to destroyed soft rock was performed, uniaxial compressive strength of specimens was recovered to some extent, while strength of primary crack zone was low to initiate larger cracks and it is the headstream of destruction. Toughness of specimens was improved significantly after grouting, it had plastic deformation ability during loading, it could absorb much energy before destruction, it also prevented destroying ahead of time from stability loss due to bearing and deforming, the effectiveness of specimens grouting were well.(4)Using numerical simulation of FLAC3 D, we carried out some research to grouting-reinforcement of main roadway side wall-rock at-850 m level in Jiulong Coal Mine. It showed that grouting reinforcement could made the energy of plastic deformation release duo to initial timbering after 200 time steps, but the roadway deformation was not convergent for a long time after grouting, and wall-rock deformation of roadway increased linearly; grouting reinforcement was adopted 800,1000,1200,1600,2000 time steps after initial timbering, because the grouting reinforcement was late, wall-rock deformation of roadway was rather larger, it lost the significance of grouting reinforcement; wall-rock deformation and distribution range of plastic zone were significantly reduced, mine anchor did not reach yield situation. Grouting-reinforcement of main roadway side wall-rock made pressure combined with compression, it improved physico-mechanical properties of wall-rock, increased self-bearing capacity and transferred back supporting pressure, it also made mine anchor exist effective tensile point in deep wall-rock and exert tensile strength, this guaranteed long-term global stability of roadway and solved grouting problem of 1000m-plus deep soft rock roadway. Through the study of side grouting-reinforcement opportunity, it indicated that 400 time steps after initial timbering, displacement of roadway two sides reduced 60% compared to initial timbering, roof and floor displacement reduced about 40%, it can reduced wall-rock deformation at the greatest extent. Combined with the observed results, best time for grouting reinforcement of main roadway was 400 time steps after initial timbering(12-18 days after initial timbering) at-850 m level in Jiulong Coal Mine.(5)The fitting data curve of two sides displacement was consistant with the curve by numerical simulation at-850 m level in Jiulong Coal Mine. fitting data and numerical value of field testing monitor mine pressure were identical, it proved that the determination method of grouting-reinforcement time was rational applying to the timeliness problem research of twice grouting, numerical software of MATLAB was used. Applying rheological theory model to analysis timeliness of grouting-reinforcement and proved effectively, deriving creep equation of roadway deformation: 0 0and strain rate equation of roadway: ε,=0.017t+58e-1.72 t. Best fitting curve showed that deformation of roadway cross-section mainly occurred ten days after excavation, deformation became relatively slow ten day later while increased at later stage, it reflected deformation characteristic of main roadway at-850 m level in Jiulong Coal Mine. When roadway strain rate was at the range of 0.1 mmd-1-0.25 mmd-1, the effect of grouting-reinforcement was the best 14 days after excavation of deep roadway wall-rock in Jiulong Coal Mine.(6) Industrial field test of grouting-reinforcement at-850 m level in Jiulong Coal Mine was performed. Synthesizing theoretical derivation and numerical simulation result, grouting-reinforcement combined with depth 14 days after initial timbering was adaptive. The concrete steps were showed below.Shallow seal and bore with mortal: slotting 45mm-dimeter and 1500mm-depth grouting holes; then tripping in 400mm-length and 42mm-diameter grouting steel tube, row spacing and vertical spacing are both 1000 mm, grouting pressure is 0.8Mpa-1.0Mpa and grouting time is about 15min; deep grouting reinforcement: slotting 45mm-dimeter and 6000mm-depth grouting holes, then tripping in 5000mm-length grouting cable anchor, vertical spacing and row spacing are respectively 1500 mm and 2000 mm, grouting pressure is 3Mpa-4Mpa and grouting time is about 20 min. Water-cement ratio was applied by the descending order, thin paste of 1:1 ratio was injected firstly, then paste of 0.8:1 ratio was injected, finally, sealing holes with paste of 0.65:1 ratio. The maximum separated strata of roof was about 2.5cm which was under control, roof wall-rock of roadway was steady. Monitoring results showed that the displacements of roadway two sides were controlled below 30 cm, the displacements of roof and floor were controlled below 20 cm, the displacements of two sides were bigger than the displacements of roof and floor, it was identical with horizontal stress where roadway located, roadway was modeled after grouting-reinforcement,roadway pressure was apparently released in later period of grouting and roadway deformation became stable 30 days later. The stress of anchor bolts became bigger obviously after grouting, the stress became steady with time, the stress in shallow part was larger than that in deeper part, the deformation of roadway became stable. Broken zone test results proved that condition of roadway wall-rock cracks were obviously improved when compared to the condition before grouting, filling degree of shallow cracks was clearer than deep one. Synthesizing results of mine pressure observation and broken zone detecting, it showed that the effect of grouting-reinforcement was remarkable, roadway timbering strength was enough to satisfy the requirement of later use, and it achieved the desired result and preserved long-term, safe and stable use of main roadway at-850 m level in Jiulong Coal Mine, it had use for reference to other similar deep soft rock roadways. |
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