Theoretical Study On Time-dependent Support Of Prestressed Anchor In Coal Mine Roadway

The excavation and support of roadways is a non-linear process.Different excavation intensity,excavation speed,excavation method,excavation technology,support timing,and support parameters result in different surrounding rock change laws and different damage degree of surrounding rock.The damage and deformation of surrounding rock are closely related to time.Due to the complex aging mechanism of surrounding rock,it is difficult to determine a reasonable support form and timing.In this paper,the change mechanism of time-dependent surrounding rock is explained from the microscopic molecular structure,the time-dependent function of surrounding rock is deduced,and the analytical calculation method of time-dependent surrounding rock is constructed.In addition,the time-dependent support mechanism of prestressed anchor bolts is studied,the analytical calculation equations of prestressed bolts are summarized,and the time variables are introduced into the analytical equations of bolts.Third,through comprehensive research methods such as theoretical calculation,numerical simulation,physical test,engineering test and field monitoring,the relevant parameters of prestressed anchor bolts are studied,which provides a basis for the establishment of time-dependent model and the design of time-dependent support;the following research results have been obtained:(1)The law of the surrounding rock disturbance boundary changing with time is studied.The distance of the disturbance boundary of the surrounding rock of the roadway is proportional to the square of time;as time goes by,the disturbance boundary of the surrounding rock gradually becomes larger,the tensile stress range of the surrounding rock gradually becomes larger,and the deformation of the surrounding rock gradually becomes larger.(2)The timeliness of surrounding rock is related to the speed of force transmission;the speed of force transmission is the sound speed of the surrounding rock;because the sound speed of hard rock is faster,so hard surrounding rock takes a short time to stabilize;because the sound velocity of soft rock is slow,so surrounding rock takes a long time to stabilize;the boundary of the traditional numerical model is fixed,but in the time-dependent model,the mechanical boundary of the surrounding rock changes all the time,and the distance between the mechanical boundary and roadway is Time is proportional to the quadratic power;different surrounding rocks and different stress environments have different quadratic time-dependent functions.(3)This paper discusses the mechanism and connotation of time-dependent support,and points out that the time-dependent of prestressed anchor bolt support mainly includes the time-dependent of the change of the bolt axial force,the and the time-dependent of the debonding failure and weakening of the anchoring interface,and the time-dependent of tray(pallet)surface.The paper determines the design method and optimal value of the initial prestress of the time-dependent bolt,proposes the control ideas and control technology of the time-dependent surrounding rock: the fundamental reason for the continuous change and development of time-dependent surrounding rock is the lack of symmetry.The response strategy of time-dependent surrounding rock is to "weaken the stress asymmetry and deformation asymmetry of the time-dependent surrounding rock in the deep and shallow parts of the surrounding rock." The control technology of time-dependent surrounding rock is super support of prestressed bolt.(4)The research results show that,after the prestressed bolt is debonded,it can still provide a part of the residual bearing capacity.The reason is that there are factors such as friction.The residual bearing capacity is an important index to improve the ultimate bearing capacity of the bolt;The rupture evolution process of the surrounding rock will reduce the confining pressure around the bolts and aggravate the debonding failure process of the bolts;the confining pressure around the bolts has a great influence on the anchoring load,but it can be significantly improved within 1MPa,and the improvement effect will be slow after 1MPa.(5)The size of the pre-stress cannot change the range of the anchoring blind zone,but can only relieve the stress environment of the blind zone.The range of the anchoring blind zone is related to the length of the anchor rod.The larger the free section of the anchor rod,the larger the anchoring blind zone.The rock mass in the anchoring blind zone is mainly maintained by the strength and self-stability of the rock itself and the surface protection mesh;when the anchoring blind zone cannot be self-stabilized,reducing the row spacing between bolts is one of the most effective methods.(6)The anchor rod axial force cannot fully represent the supporting conditions of the anchor rod.The deformation,creep and stress evolution of the pallet are also important factors;the stress distribution law of the pallet is generally large in the middle and small at the edge,which is not conducive to anchor support.The more uniform the stress of the pallet is,the more favorable it is,and the more concentrated it is in the middle position,the more unfavorable;the larger the size and thickness of the pallet,the faster the resistance of bolt support increases during the deformation of the surrounding rock,and the more effective it is to control the deformation of the surrounding rock;The large pallet has a large force area and a wide control range,which is conducive to improving the ability of surrounding rock protection,but it is not conducive to the optimization of the force of the pallet itself(the edge torque is too large).(7)Put forward the concept of super bolt support,design the group anchor structure to realize super support,and conceive the supporting group bolt construction machine tool.The research results show that the super prestressed bolt has a good supporting effect;the center point support of the super bolt can optimize the supporting parameters mechanically to the greatest extent.It can not only expand the row distance between the bolts and accelerate the construction speed,but also reduce the range of loosening and damage of surrounding rock;the stress concentration at the tail of the super bolt is very obvious,and the traditional pallet is not conducive to the maintenance of the super prestress.The new group bolt structure can effectively weaken these adverse effects.(8)The calculation software of the time-dependent support model is programmed.The software can not only simulate the changing rule of roadway surrounding rock under the action of time,but also simulate the whole process of excavation,support,stoping and the next working face.The software is based on the analytical calculation equation,and the calculation speed is fast,which can realize the solution of the supersize model.Moreover,there is no limitation on the size of the model theoretically,and the size of the calculation model can be flexibly scaled according to the size of the research object.This dissertation totally have 87 figures,5 tables,and 217 references,respectively.