The Reasonable Thickness Of Shotcrete Layer In Deep Soft Rock Roadway

With the increasing demand energy,the scale of coal mining is becoming larger and the excavation depth is becoming deeper.Nearly 53 % of the mining area in China has been mined at depths of more than 800 meters,while 70 % of deep roadways are arranged in weak coal seam.Taking certain measures to guarantee the stability of roadway surrounding rock has important economic benefit and safety value to the construction and production of coal mine.The numerical model of reasonable strain softening is established by using theoretical analysis and numerical simulation with FLAC3 D.Based on the numerical simulation,the plastic range and displacement field as well as stress field distribution of surrounding rock in different injection bed thickness are studied.The influence of injection thickness on the stability of roadway surrounding rock was analyzed under different depth of roadway and section size of roadway.In this paper,the depth of roadway is 600.0m,8000.0m and 1000.0m respectively.The broken face of the roadway is a half arch of straight wall,and the section size of roadway can be divided into three situations: 1)width 6m,straight wall 3m,semicircular arch 3m;2)width 8m,straight wall 4m,semicircular arch 4m;3)width 10 m,straight wall 5m,semicircular arch 5m.The displacement field,stress field and the distribution law of plastic ring in roadway surrounding rock simulated while the thickness of concrete spray are 0.0mm,20.0mm,50.0mm,70.0mm,100.0mm,200.0mm,300.0mm,400.0mm respectively.The following results were obtained by numerical simulation:(1)When the embedment depth of roadway surrounding rock is the same,with the increase of surrounding rock section size,the effect of the size of the spray layer thickness on the stability of surrounding rock of roadway is more and more obvious.The effect of the spray layer thickness on surface displacement control is the most obvious.When the roadway section size is the same,with the increase of buried depth of surrounding rock,the influence of the size of the spray layer thickness of roadway surrounding rock stability is more and more obvious.The effect of the spray layer thickness of surface displacement of roadway control was the most obvious.(2)For the section size of deep roadway under the conditions of the same,when buried deeply 800.0m to 1000.0m,reasonable spray layer thickness is 200.0mm.With the continue increase of buried depth,spray layer thickness has minimal impact to the stability of surrounding rock.For the same depth of deep soft rock tunnel(Taking the buried depth 800.0m of excavation roadway as an example),with the increase of roadway section size,reasonable spray layer thickness is about 200.0mm.When the section size continues to increase,spray layer thickness has minimal impact to the stability of surrounding rock.(3)The plastic distribution of the surrounding rock and the displacement of the roadway surface of different injection thickness near the intersection of the straight wall and the semicircular arch,where is the key part of the roadway wall rock which is prone to instability are larger than other places.Reasonable support form and parameters should be chose according to strength requirement in numerical simulation.Spray thickness of deep soft rock has significant effect on the plastic range and the displacement and stress of key part of roadway surrounding rock.