Study On The Stability Mechanism Of The Anchorage System For Surrounding Rock Of Deep Roadway Under Cyclic Cutting

During the stage of excavation,the deep buried roadways begin to deform and fracture.In the later stage of excavation,the deformation becomes so severe that the full section weighting occurs,resulting in great difficulty in supporting.The deformation of the roadway starts from excavation and originates from disturbances.Moreover,the multiple disturbances generated by cyclic cutting during excavation are regarded as the leading inducements that results in initial damage and later instability of the anchorage system.Differing from conventional low stress roadways,the surrounding rocks of deep buried high stress roadways are more sensitive to disturbances so that they are more prone to suffer from small deformations and fractures.As the damage continues to evolve,it exerts negative impact on roadway bearing capacity in the long-term.Therefore,based on the characteristics analysis of the driving disturbance in deep buried roadway excavation,it is of important scientific significance to research the damage mechanism of the anchorage system and anti disturbance support principle during cyclic cutting.Taking the deep buried roadway in Menkeqing Coal Mine as the engineering background,this paper use field investigation,numerical simulation,theoretical analysis,physical and mechanical experiments,industrial experiments,and other methods to study and reveal the stability mechanism of cyclic cutting in deep buried roadways surrounding rock anchorage system,and forms control countermeasures to resist cyclic cutting.The main conclusions obtained are as follows:(1)The deformation and failure characteristics of the initial anchorage system during deep buried roadway excavation are expounded.The deep buried roadway suffers serious deformation and damage during excavation,and the maximum development height of roof separation fracture is 3.23 m.The initial anchorage system of deep buried high stress roadway is defined,and the influence of key factors such as the stress environment on the initial anchor system of high stress roadway is also expounded:(1)Under high stress environment,the intensity of cyclic cutting disturbance is huge.(2)The thickness of the bearing ring of the head-on roof support is small and its anti-interference ability is also weak.(3)The support efficiency of a single bolt is low,the overall support density is high,and the excavation-support speed is slow.(4)The excavation speed is slow,the driving disturbance cycle is long,and the damage of the anchorage system is serious.(2)The stress transfer characteristics of rock cutting disturbance in the front of deep buried roadway are revealed.Periodic cyclic cutting inevitably leads to periodic damage on the shallow rock mass of the head-on roof.The cutting disturbance stress decreases with the increase of the lagging head-on distance,and the stress attenuation curve conforms to a “power exponential composite function”,whose expression is.Combined with the conditions of main haulage roadway 11-3108 in Menkeqing Coal Mine,the near,medium,and far field disturbance areas for cyclic cutting are delineated.The corresponding relationship between driving disturbance stress and core parameters such as excavation section,driving depth,and unloading speed are studied.It is clear that the main driving parameter that affects the strength and transmission range of cutting disturbance stress is unloading speed.(3)The disturbance law of cyclic cutting on adjacent initial anchorage systems is revealed,and the direction of intelligent decision-making under the evaluation of anchorage system time stability is also clarified.(1)Due to periodic loading and unloading,cyclic cutting causes periodic disturbance to the anchorage system.As the heading continues(the disturbance weakens),the periodic loading and unloading phenomena in the distance disappear.The area with obvious periodic loading and unloading effect is defined as the initial anchorage system zone,and a method for delineating the length range of the initial anchorage system of deep buried roadway is also proposed.(2)The influence of excavation speed on the length range of the initial anchorage system is relatively small,however,accelerating the excavation speed can not only reduce the disturbance time of the anchorage system,but also reduce the fluctuation amplitude and stability value of the anchor cable load.(3)The initial damage of the anchorage system can be controlled by increasing the length of the bolt or the length of the anchor section during cyclic disturbances.(4)The status information of anchor rock mass that needs real-time monitoring during roadway excavation and support is explored.Besides,the adaptability of the support scheme is determined based on the monitoring results.Based on the suitability evaluation results of surrounding rock support schemes and the real-time detection results of occurrence information of surrounding rock in the head-on roadway,a framework for intelligent decision-making and optimization of support schemes is formed,which can provide ideas for intelligent judgment of the suitability of support schemes in coal roadways and the implementation of intelligent decision-making.(4)The formation principle of the prestress bolt anchorage blind zone is clarified.Moreover,as the five support parameters such as prestress change,the relationship between the rock mass stress and distribution range in the anchorage blind zone is also explored.It is concluded that the main factors affecting the stability of the anchorage blind zone are bolt length,prestress,and bond length.The height range of the anchorage blind zone in this geological condition of this project is approximately40-60 cm.The superimposed perturbation mechanism of cyclic cutting on anchorage blind zone is revealed: cyclic cutting causes fluctuating unloading effect of rock mass stress in the anchorage blind zone due to repeated tension and compression;moreover,the rock mass undergoes multiple shear tensile failures,and the anchoring blind zone structure experiences multiple fractures and eventual loosening.Four countermeasures have been proposed to address the problem of rock fragmentation and cracking in the anchorage blind zone during cyclic disturbances.(5)The relationship between key anchorage parameters and the anti disturbance performance of the anchorage body is experimentally studied.(1)As the bolt length increases,the anchorage system undergoes a stress yielding stage,whose emergence trend shows more obvious as the length of the bolt increases.After the peak,the phenomenon of tension fluctuation exists,and the tensile force also increases with the length of the bolt.(2)Increasing the bolt length and the anchor section can enhance the peak strength of the anchor rock mass.Besides,increasing prestress can effectively enhance the strength of the anchor body,however,the strengthening effect of the anchor body gradually weakens with the increase of support strength.(6)The anti disturbance control technology for deep buried roadway is proposed.The time-dependent characteristics of excavation and support in deep buried roadway are analyzed.Moreover,this paper divides the cyclic cutting disturbance area into three zones to form regional zone control strategies.The principle of efficient cross-boundary anchoring control technology for thick layers is proposed.By constructing a thick anchorage layer of the roof,the small displacement of the deep stable rock mass can limit the large displacement of the shallow damaged rock mass,so as to realize the linkage of the large and small displacement of the deep and shallow rock mass.As a result,progressive damage and failure of rock mass from shallow to deep can be controlled.The high-efficiency and low-density excavation and support collaborative technology has been proposed.Through cross-boundary anchorage control technology for thick layers,the higher support efficiency of single bolt as well as lower support density can not only improve group anchorage effect,but also accelerate excavation speed.That is to say,the disturbance impact of cyclic cutting is weakened from two aspects of efficient excavation and support.(7)Industrial experiments on anti disturbance support for deep buried roadways are conducted,and a support scheme of high efficiency and low density is developed.The length of the flexible anchor resin anchorage section is determined through experiments.Results show that the anti disturbance performance and stability of the roadway are significantly improved with new support scheme,and the roof separation cracks is also effectively controlled.The excavation speed has been increased from650 m/month to 1040 m/month,realizing efficient disturbance resistance control in deep buried roadways.This paper has 87 images,13 tables,and 131 references.