Study On Anchorage Control Of Surrounding Rock In Gob-side Driving Of Fully Mechanized Sublevel Caving In “Three Soft” Thick Coal Seam

Zhaojiazhai mine of Zhengzhou Coal Group is a typical “Three Soft” thick coal seam.The average thickness of top coal in the mining roadway varies from 2?3m,and the local section of gob-side entry driving was seriously damaged,which affects the normal use of the site.During the construction of bolt-mesh-anchor support,there are some problems such as poor quality of hole formation,serious hole collapse and low anchoring force,especially the small coal pillar near the goaf.Therefore,based on the existing geological mining conditions of Zhaojiazhai coal mine of Zhengzhou Coal Group,in this paper,by using field observation,theoretical analysis,numerical simulation,similar simulation and field test,the law of mine pressure appearance in gob-side entry driving of fully mechanized top coal caving face in“Three Soft” thick coal seam,and anchoring mechanism,technology and equipmentof drilling-sealing-injection integration in soft and broken coal body were researched systematically.The main achievements are as follows:(1)On the basis of field observation,the deformation and failure characteristics of the surrounding rock in gob-side entry driving with small coal pillars was analyzed,and the results show that the deformation of the surrounding rock in gob-side entry driving is asymmetrical,and the deformation value and vertical stress on the side of the small coal pillars are large;the plastic area of the surrounding rock is large,and the small coal pillars completely present plastic state,and there is a shear zone in the small coal pillars,which may lead to shear instability of the small coal pillar.(2)Based on the self-designed drilling-sealing-injection integration extendable bolt,anchoring mechanism of drilling-sealing-injection integration in small pillar roadway along goaf in fully mechanized top coal caving face of “Three Soft” thick coal seam was expounded through theoretical analysis.The strength and size of drilling-sealing-injection integration extendable bolt body and connecting piece were optimized,the optimal grouting pressure was determined,and the relationship between sealing length and sealing effect was analyzed.It is found that the expansion range of gounting crack is large in soft coal.After grouting is stable,the porosity and stress of soft coal is the highest,followed by that of medium soft coal,and that of hard coal is the lowest under the same measuring circle.(3)A integrated test bench of grouting and anchoring technology has been independently developed.According to the vibration monitoring of drilling sealing injection integrated anchor rod,it is found that the longitudinal vibration acceleration value of the rod in the soft coal body is far greater than that ofthe broken coal body during the drilling,which provides a basis for identifying the integrity of the coal body.Through the ultrasonic non-destructive testing of the grouting effect,it is found that bearing body can be formed within the anchorage range after grouting.Compared with the test results of bolt drawing in broken coal and soft coal,it is found that the average value of the peak value of bolt drawing force in soft coal is greater than that in broken coal,which indicates that the quality of grouting and anchoring in soft coal body is better,so the bearing capacity of anchoring system is higher.(4)The dring sealin injection integrated anchoring test was carried out on the side of coal pillar of gob-side entry driving in the underground field,which verified the results and effectiveness of the laboratory experiment.The test results show that the average peak value of the anchoring force after grouting at each station is significantly higher than that of the resin anchored bolts near the same station,and the lateral deformation of coal pillar is small.Considering that the bolt body is hollow,the sealing hole is rubber sleeve,and the drill bit is made of thin steel pipe,therefore,the cost of dring sealing injection integrated extendable bolt is equivalent to that of ?20mm threaded stell bolt of the same length,which is helpful to reducethe cost of roadway support and repair.