Anchoring Performance Of Micro NPR Anchor In Sujiapo Phosphate Mine

With fewer and fewer shallow buried mineral resources and more and more people needing these resources,many countries in the world have taken the depth of mineral resources from shallowly buried positions to deep buried position.In the deep mining environment,the frequency and disaster degree of engineering accidents caused by the failure of traditional bolts is increased due to the insufficient material properties of the bolt.The buried depth of the working face 270 in the Six Pan area of the Sujiapo phosphate mine is 980 m,and the ground stresses in the vertical and horizontal directions are 26.46 MPa and 41.16 MPa respectively,which belong to the extremely high ground stress area.The roof surrounding the rock of the working face is dolomite,and the ultimate compressive strength can reach 202.20 MPa,belonging to the category of hard rock.However,due to the influence of large engineering buried depth and high ground stress,it belongs to engineering soft rock.Under the original support mode,deformation problems such as roof subsidence,roof collapse,local falling block,sheet wall,and rock bursts often occur in the working face.Later,based on the active support concept,a micro-NPR new material anchor bolt is used for support.Based on the engineering background of the roadway at 270 working faces of the deep-buried Sujiapo phosphate Mine,this thesis carried out a series of studies on the anchorage performance of the micro-NPR new material bolt applied by it and its influence on the stability of the roadway surrounding rock.By carrying out the indoor static tensile test,the distribution law of anchorage force,micro-strain,shear stress,axial force,and interface bond strength of bolt under different bolt diameters,anchorage lengths,and anchorage materials are analyzed,and reasonable bolt diameter,anchorage length,and anchorage materials are determined based on the drawing test data,which provides important guiding significance for NPR active support design of rock in phosphate mine roadway.Finite element software ABAQUS was used to establish a two-dimensional numerical calculation model of the roadway under non-support,non-prestressed bolt support,and micro-NPR bolt active support,and to compare and analyze the effect of micro-NPR bolt controlling the deformation of roadway surrounding rock in a deep-buried phosphate mine.Finally,the field test was completed based on the results of the indoor drawing test and numerical simulation.The conclusions drawn from the above research are as follows:(1)Under uniaxial compression,the peak axial stress of dolomite can reach 202.20 MPa,and the failure mode is mainly fracture.The change process of the stress-strain curve can be divided into three stages: linear elasticity,plasticity,and crushing.In this paper,the dolomite in the Sujiapo phosphate mine project is affected by high-ground stress,and the dolomite with the characteristics of hard rock has become the characteristics of soft rock.The deformation problems such as roof subsidence,roof collapse,local falling block,pillar,roadway slabs and rock bursts often appear.(2)Under different bolt diameters(18 mm,22 mm),anchoring lengths(300 mm,400 mm,500 mm,600 mm),and anchoring materials(M30,M40,M50 cement mortar,2350 resin anchoring agent),the failure form of micro-NPR anchor solid is the sliding failure of the interface between bolt-anchoring material.The anchorage force-displacement curve can be divided into the elastic stage,constant resistance stage,and slip stage.The microstrain and axial force of the micro NPR bolt increase with the increase of the loading load at the same position and show an increasing trend from the anchoring bottom end to the anchoring start end.The ultimate anchoring force and peak displacement of the micro NPR bolt are positively correlated with the diameter of the bolt,anchoring length,and cement mortar strength.Under2350 resin anchoring agent,the ultimate anchoring force of the micro NPR bolt is 200.99 k N,1.23 times,1.01 times,and 0.91 times of that under M30,M40,and M50 cement mortar anchoring,and the peak displacement is 53.21 mm.It is 3.83 times,2.44 times,and 2.13 times of M30,M40,and M50 cement mortar anchorage.The peak values of microstrain and axial force are 7918.04με and 30.22 k N respectively,which are 0.71 times,0.93 times,and 1.05 times of those under M30,M40,and M50 cement mortar anchorage.(3)Under different bolt diameters(18 mm,22 mm),anchoring lengths(300 mm,400 mm,500 mm,600 mm),and anchoring materials(M30,M40,M50 cement mortar,2350 resin anchoring agent),the shear stress at the same position of the interface between micro NPR bolt and anchorage material increases with the increase of loading load.When the diameter of the micro NPR bolt is 18 mm,the shear stress curve of the same loading load decreases first and then increases from the bottom end to the beginning end of anchoring.When the diameter of the micro NPR bolt is 22 mm,the shear stress curve of the same load increases first and then decreases from the bottom end to the beginning end of anchoring.Under the combined action of different anchoring lengths and different loading levels,the shear stress on the interface between the micro NPR bolt and anchoring mortar basically decreases first and then increases,and the individual shear stress curves decrease first and then increase and then decrease from the bottom end to the beginning end of anchoring.The bond strength between the interface of the micro NPR anchor and anchor layer is negatively correlated with the diameter of the anchor bolt,but positively correlated with the anchorage length and strength of the anchor layer.(4)In order to solve the deformation problem of the Sujiapo phosphate mine,a support scheme with micro NPR anchor as the main body and steel mesh + shotcrete as the auxiliary is developed.The simulation results show that,on the one hand,the large deformation of the dolomite roadway under the influence of high-ground stress can be eliminated under the support scheme,and the roof subsidence and the shrinkage of the left and right sides of the roadway can be effectively controlled.On the other hand,the asymmetric deformation of the left and right sides of the dolomite roadway is effectively solved.The cohesiveness and strength of surrounding rock are enhanced effectively so that the deformation of surrounding rock is controlled within a reasonable range.(5)Field monitoring data showed that under the micro-NPR anchor active support,the roof settlement and the shrinkage of the two sides of the roadway increased at a faster rate in the first 15 days,and the increase rate gradually decreased in the next 15 days.Finally,the roof settlement and the shrinkage of the two sides of the roadway tended to be constant on the25 th day.The final settlement of the roadway roof is 59.84 mm,and the shrinkage of the left and right sides is 43.68 mm.The deformation of the roof and surrounding rock of the two sides is within the controllable range.