Research On Optimization And Engineering Application Of Bolt Support In High Stress Soft Rock Roadway

Anhui province and Shandong province are important energy bases in China.As the mining depth of coal mines increases,deep mine soft rock roadways begin to face in a high-stress environment,with serious deformation and difficult support issues,resulting in frequent roadway repairs and loss of anchor bolt safety.Correpondent accidents increases as well,which seriously threatens the roadway construction and the personal safety of construction workers.Based on the results of in-situ stress test of mining areas in Anhui Province and Shandong Province,this paper clarifies the distribution characteristics of in-situ stress fields in mining areas.Taking Pansan Coal Mine,a key coal mine in Huainan Mining Area,Anhui Province,as an example,the in-situ stress of Pansan Coal Mine was measured,and the evolution law of the surrounding rock stress and the anchor axial force when the axial direction of the roadway was different from the maximum horizontal principal stress direction was simulated.It is found that the deformation of the roadway is not only related to the magnitude of the ground stress,but also to the axial direction of the roadway layout and the direction of the ground stress field.Traditional anchor support measures fall behind the current roadway support requirements.By analyzing the effect of anchoring factors through orthogonal tests,and improving the bolt support technology.An optimal bolt anchoring scheme is proposed.The optimized bolt anchoring scheme obtained by the research is applied to the support of high stress soft rock roadways,and works well which can offer reference for bolt support of soft rock roadways in mining areas of Anhui Province and Shandong Province.The main research results are as follows:(1)According to the results of in-situ stress measurements in Anhui and Shandong mining areas,it is found that Anhui and Shandong mining areas are high geostress mining areas with mainly horizontal stress.Taking the Pansan Coal Mine as an example,in-situ stress measurement using the stress relief method at Pansan Coal Mine show that Pansan Coal Mine is a high-in-situ stress mine with a large stress difference.According to the in-situ stress distribution law of Pansan Coal Mine,the mine takes the south-north horizontal stress as the maximum principal stress.Deformation of the roadway increases rapidly when the angle formed by the mine high ground stress soft rock roadway and the sharply direction of the maximum horizontal principal stress is an unfavorable angle.(2)The numerical simulation of the anchoring and supporting effect of the roadway is made by changing the angle formed by the roadway layout direction and the horizontal maximum principal stress,and bolt simulation adopts extended anchoring method.The research shows that when the angle between the roadway layout direction and the horizontal maximum principal stress direction is between 0 ° and 30 °,the stress of the surrounding rock of the roadway is relatively relaxed.While the angle is greater than 30 °,the stress at the top and bottom of the roadway significantly increases and the stress concentration increase.The overall axial force of the anchor rod is distributed in a "?" shape.The axial force of the anchor bolt of the side is negatively related to the increase of the included angle formed by the axial direction of the roadway with the horizontal maximum principal stress.The axial force of the top anchor is opposite to that of the axial force of the anchor bolt.The support effect of the surrounding rock of the roadway is reflected by the stress state of the anchor rod.When the included angle is greater than 30 °,the roof of the roadway gradually becomes the support point.(3)When high-stressed soft rock roadways are supported by extended anchor bolts or full-length anchor bolts,there are problems of low anchor bearing capacity and uneven force in the anchoring section,and it is impossible to achieve the need to suppress large deformation of the roadway through anchor support.Orthogonal scheme is used to design the pull-out test of anchors with different anchoring factors.The test results show that the failure of the anchor rod first occurs at the bonding interface between the anchor body and the test block.The anchor rod and the test block undergo 6 dynamic stages of the elastic-plastic-destruction from the beginning of the drawing to the failure of the anchor.The combination of different anchoring influencing factors has different effects on anchoring failure and the ultimate pullout force of the anchor.The strength of the test block and the prestress of the anchor have a significant effect on the ultimate pullout force of the anchor.(4)According to the action of anchoring influencing factors,a high-prestressed post-tensioning method for full-length anchoring support was proposed,a high-prestressed anti-friction shim and a new type of full-length anchoring bolt were developed accordingly.Based on the analysis of the mechanical characteristics of the full-length anchor support with high prestressed post-tensioning method and the theoretical calculation of the bearing capacity of the surrounding rock,and the use of force-measuring anchors and traditional extended,full-length anchor support in indoor and field tests are carried on to make comparison.Due to the high-prestressed support and full-length anchoring support of high-prestressed post-tensioned full-length anchoring support method,,the prestress can be transmitted into the surrounding rock,increasing the range of surrounding rock pressure stress zone,so that it can form a more effective anchoring surrounding rock bearing structure,and effectively control the surrounding rock deformation in field experiments.The high prestressed post-tensioning full-length anchoring support method makes the distribution of the shear stress at the anchoring interface smoother,reduces the occurrence of stress concentration,and avoids the occurrence of an anchor loss and anchor loss accident.(5)The mechanical mechanism of the surrounding rock-anchor of the deep-buried circular roadway under the non-uniform stress environment is analyzed.Considering the softening effect and expansion effect of surrounding rock and the anchoring effect of anchor,the expressions of stress and displacement in the elastic-plastic zone of surrounding rock under different horizontal stresses and the analytical expressions of anchor force are derived.The analysis is made from four aspects: surrounding rock lateral pressure coefficient,anchor prestress,surrounding rock strength and anchor length.The lateral pressure coefficient is the main factor affecting the shape of the roadway's anchorage crushing zone.The difference in the shape of the anchorage crushing zone results in different force distribution of the anchor rods at different positions in the roadway.The difference in the shape of the anchored broken zone results in different force distribution of the anchor rods at different positions in the roadway.The key to controlling the deformation of the roadway is to suppress the deformation of the roadway by using the anchor support.Increasing the prestressing force of the anchor rod and improving the strength of the surrounding rock can significantly improve the support quality of the anchor rod.Only changing the length of the anchor rod has little effect on the support effect.(6)According to the geological environment of high geostressed soft rock roadway and the existing surrounding rock classification standards,the dynamics based on the premise of in-situ stress measurement and the full-range monitoring of force-measuring anchors with high prestressed full-length anchoring technology as the core and corrected by numerical simulation Support optimization design scheme.Through local support and strengthening design for the key support areas of the roadway,the results show that the support optimization scheme significantly improves the surrounding rock characteristics,reduces the deformation of the roadway by increasing the effective compressive stress of the surrounding rock,and improves the anti-deformation ability of the surrounding rock.