The Mechanism Research And Engineering Application Of Bolt-grouting Reinforcement For Fractured Rock Mass Based On Prestressed Anchor And Self-stress Grouting

Underground engineering activities often encounter bad geological fractured rock masses.Grouting reinforcement can block the fractures of the rock mass and improve the mechanical properties of the fractured rock mass.Aiming at the problems of grout-rock interface loosening and unsatisfactory filling caused by self-shrinking of cement-based materials for the grouting of underground fractured rock mass,this paper proposes a self-stress grouting reinforcement method and bolt-grouting reinforcement method for fractured rock mass based on prestressed anchor and self-stress grouting.The volume expansion of the slurry stone body in the confined space is promoted by the admixture,which compensates for the self-shrinking of the cement-based material while generating an expansion pressure.This improves the compactness of the slurry stone body and improves the stress state of the solidified body.The self-stress of the slurry stone and the axial stress of the anchor are used to strengthen the rock mass together,so that the solidified body is in a quasi-3D stress state.This restores the stress state of the original rock to a certain extent,and greatly improves the reinforcement effect of the fractured rock mass.Through theoretical analysis,laboratory tests,numerical simulations,engineering applications,and so on,the mechanism of bolt-grouting reinforcement for fractured rock mass based on prestressed anchor and self-stress grouting was investigated.The main results were as follows:(1)The principle of self-stress slurry reinforcement for fractured rock and bolt-grouting reinforcement for fractured rock mass based on prestressed anchor and self-stress grouting were analyzed.The advantages of self-stress slurry-reinforced rock mass include:the compactness and strength of the slurry stone are improved,and the stress state of the consolidated body formed by the slurry stone and the fractured rock is improved.The expansion stress of the slurry stone and the axial stress of the bolt have an additive relationship with the increase of the maximum principal stress of the fractured rock.As the distance between the rock mass and the slurry stone increases,the additional stress generated by the expansion stress gradually decreases.And the additional stress is positively correlated with the volume of the slurry stone.The relationship between the axial stress of the bolt and the interface shear stress before and after the prestress loss was analyzed.The relationship between shear stress and shear displacement of the anchoring section of the bolt before and after de-anchoring was studied.(2)Through the longitudinal free expansion rate test,the strength test of the constrained slurry stone,and the micro analysis of the constrained slurry stone,the swelling performance and strength characteristics of the self-stress cement slurry were studied.As the content of expansion agent increased,the free longitudinal expansion rate of the slurry stone and the strength of the constrained stone increased first and then decreased.The best content of expansion agent for self-stress grouting material was 10%.The longitudinal free expansion rate of the ultrafine siliceous slurry with 10%expansion agent was 1.94%.The peak strength of self-stress slurry stones under restraint was 50.37%higher than that of ordinary slurry stones.The self-stress ultrafine Portland cement slurry stone particles overlaped each other to form a network structure,and its compactness was obviously better than that of ordinary slurry stone bodies.(3)The prefabricated fractured rock masses with different lithologies reinforced by ordinary slurry and self-stress slurry were selected for uniaxial compression test and acoustic emission test.And the bolt-grouting test of the prefabricated cracked sandstone was carried out.For various lithological samples,the self-stress slurry was better than ordinary grouting in reinforcing the prefabricated fracture samples.As the strength of the rock mass decreased,the strength reduction factor of the grouting-reinforced rock specimens tended to increased.The restoration degree of grouting reinforcement to the strength of different lithological fractured rocks was ranked as sandstone<carbonaceous mudstone<sandy mudstone<coal.As the strength of the rock gradually weakened,the failure form of the slurry-reinforced rock mass gradually transitioned from shear-slip failure along the diagonal to splitting and collapse failure.After the cracked sandstone reinforced by bolt-grouting reinforcement passed the compaction stage and the elastic deformation stage to the peak strength,a significantly longer post-peak delayed deformation appeared.The higher the anchoring strength of the sandstone reinforced by the slurry,the greater the increased in its peak strength.The peak strengths of the new prestressed bolt-grouting sandstone reinforced by one and two anchor rods were 13.59%and 12.65%higher than those of ordinary bolt-grouting specimens.The advantages of new prestressed bolt-grouting for reinforcing sandstone were obvious.(4)Through numerical simulation,the effects of crack parameters such as crack dip angle,crack opening and crack roughness on peak strength,peak strain and elastic modulus of rock mass reinforced by ordinary slurry and self-stress slurry were studied.When the fracture inclination angle θ is θ1<θ<θ2,the grouting reinforced fractured rock appeared to be dominated by shear-slip failure along the interface of the slurry-rock,while the other angles were dominated by overall split failure.The peak strength and peak strain of the rock reinforced by the two slurries showed a trend of decreasing first and then increasing with the increase of the fracture dip angle.The peak strengths of ordinary slurry-reinforced rocks and self-stress slurry-reinforced rocks with different fracture apertures were basically around 3.30MPa and 3.65MPa,respectively.The peak strength and peak strain of the rock mass reinforced by the two slurries gradually decreased with the decrease of the fracture surface roughness.The peak strength and peak strain of self-stress slurry-reinforced rock mass with the same fracture dip angle,fracture opening and fracture roughness were greater than those of ordinary slurry-reinforced rock mass.(5)Using ultra-fine cement,modified clay,silica fume,expansion agent,water-reducing agent and quick-setting agent as raw materials,ultra-fine silicon self-stress composite grouting reinforcement material was developed through orthogonal test.The contents of superfine cement,clay,expansion agent,silica fume,setting agent and water reducer were 79%,5%,10%,6%,2.9%,2.5%,respectively.The material had the characteristics of fast initial setting,good fluidity,good expansion and high strength.(6)Based on the analysis of the surrounding rock fragmentation mechanism and the evaluation of the original support method,the bolt-grouting reinforcement method based on prestressed anchor and self-stress grouting was used to control the surrounding rock in the substation roadway of Pingmei No.10 Mine.A high-strength prestressed grouting bolt system and a new bolt-grouting support scheme were designed.After the new bolt-grouting reinforcement,the grouting veins filled the surrounding rock cracks.The slurry had good diffusibility.The structure of the slurry-filled calculi was dense and the particles were relatively uniform.The prestressed grouting bolt and cable were stable under stress.The deformation of loose and broken surrounding rock within the anchorage range was effectively controlled.The deformation of the substation roadway gradually stabilized.The maximum displacement of the surrounding rock on the surface was 83mm,and the deformation of the surrounding rock was not large,which truly achieved zero repair after roadway maintenance.