| Coal-bearing strata tunnels are common in mountain tunnels,and the strata conditions of coal-bearing strata tunnels are complex.In the process of construction,gas leakage,explosion,coal seam outburst,extrusion,compression and other geological disasters pose potential threats to the safety of personnel and equipment,and increase the construction risk.Therefore,it is necessary to formulate a safe and reliable technical scheme for tunnel blasting in coal-bearing strata to avoid accidents such as coal and gas outburst caused by blasting operations,which has practical economic significance for ensuring safe and efficient construction.Based on the Guigala tunnel project on the S5 line of the Lhasa to Zedang expressway in Tibet,the following research results are obtained by using rock mechanics,explosion dynamics,structural mechanics,elasticity theory,coal and gas outburst theory,mine pressure theory,controlled blasting theory,field test and numerical analysis methods:The leading factors of coal outburst in rock cross-cut of tunnel were the proliferation of cracks between coal seam and rock strata,the compression of roof and floor of coal seam and the creep fracture failure of rock column under dynamic load of blasting;Calculation of different diameter 3 coal mine permissible emulsion explosive blasting in Ⅳ level of rock and coal area,determine the cut hole and caving hole smaller uncoupling coefficient,smooth blasting hole and coal seam hole choose larger uncoupling coefficient.All the holes adopt forward initiation charge structure,and the quantity of water stemming was 1 section.The cutting efficiency and blasting vibration effect of second-order second-stage cut with different parameters were studied for the first time,and the charging diameter of the central hole in the whole rock section before uncovering coal was 32 mm,the vertical depth of the first-order hole was 1.2m,and the dip Angle of the first-order hole was 70 degrees;Innovatively studied the cutting efficiency,the depth of coal seam and the disturbance degree of coal seam and its roof with different cutting parameters of rock cross-out straight cut.It was found that the hollow hole radius was 60 mm and the distance between cut hole and hollow hole was 24cm;In view of the whole rock section,the fracture situation of smooth blasting layer,the number of remaining holes and the damage depth of rock outside the contour line were analyzed,and cutting seam cartridge was used in smooth blasting hole and the hole spacing was 70cm;Considering the weakening effect of gas pressure on the mechanical parameters of coal body,it is applied to the parameter design of coal seam periphery in tunnel.By numerical example comparison,the fracture situation of smooth blasting layer,surrounding flatness and damage depth of coal body outside the contour were analyzed,and the surrounding hole spacing was40 cm,the offset distance of contour line was 20 cm,and the thickness of smooth blasting layer was 50 cm.Moreover,when the gas pressure is 1MPa and 2MPa,the blasting damage depth of coal seam increases by 19.5% and 35.5% respectively.According to the blasting operation of the uncovering coal at rock cross-out of Guigala tunnel,the blasting damage depth of the rock column is 0.86 m by numerical example,and the minimum safety thickness of the reserved rock column is deduced by using structural mechanics under the action of ground stress and gas pressure,and the thickness calculation formula of the reserved safety rock column for the blasting of the tunnel with different dip coal seams is ? [ ]?hhhhD,maxsin23(10)(28)?;The dynamic response of the micro-differential interval time to the steep,inclined and gently inclined coal seam and its roof and floor was creatively studied,and the optimal interval time was all 35 ms.With the dip angle of coal seam increases,the vibration velocity,acceleration and effective stress attenuation rate accelerate,the dynamic response degree of floor increases significantly,and the increase of disturbance degree of coal seam and roof is small,and the disturbance degree of large dip seam and roof and floor is the most significant;Aiming at the blasting operation after debunking the coal seam,the influences of footage and the maximum blasting dose of a single section on the blasting vibration of the tunnel lining of coal seam were analyzed,and the footage was 2m,the blasting dose of a single section was not more than 27.9kg.The blasting parameters of the whole rock section,rock cross-out section,half coal rock section and coal seam section of Guigala tunnel are given,and the blasting test in the whole rock section verified the rationality of the research results;The blasting vibration was monitored,and the least square method was used to carry out regression analysis on the monitoring data,and the tunnel site coefficient K was 43.46 and the vibration attenuation coefficient α was 1.089;Based on the HHT method,MATLAB is used to analyze the frequency spectrum of the vibration signal,and it’s concluded that the blasting vibration energy is mainly concentrated in 10~75Hz. |
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