Research On Theory And Practice Of Mining Legacy Strip Pillar With Paste Backfilling

It is one of the main methods of Three Under coal mining to recycle the left stripcoal pillars by paste filling. Paste filling mining can achieve the best effect insubsidence control. But in the meantime, the method faces great pressure of reducingcost and promoting efficiency. Based on the characteristics of recycling strip coalpillars by paste filling, the dissertation has made analyses and researches from thefollowing aspects:(1) Having made up the new type of rapid hardening paste fillingmaterial, which provides the condition to shorten the cycle of filling mining.(2)Having put forward the method of determining the supporting strength of fillingworking face for the sake of subsidence control and working face safety, whichprovides the theoretical basis for enhancing hydraulic support design and reducingmanufacturing cost.(3) Having built the interaction model of the filling body and theimmediate roof according to the moving and deforming rules of paste filling workingface roof, which provides the basis for matching filling interval and the early strengthperformance of paste material.(4) Having verified the influence of goaf activation bysimulation tests and put forward the evaluating method of activation degree, whichprovides references for subsidence prediction of recycling strip coal pillars by pastefilling.We have developed cementing paste and rapid hardening paste on the basis ofconventional cement paste and have tested the mechanical performance indexes of thethree types of paste. The result suggests that cementing paste and rapid hardeningpaste have such qualities as rapid hardening and high strength at early period whichprovides the condition to shorten the cycle of filling mining. They represent thedeveloping direction of paste material.One of the differences between filling mining and caving mining is that thedesign of supporting strength on the paste filling working face has to meet therequirements of controlling overlying rock and subsidence and resisting the lateralpressure of paste. The dissertation puts forward the theoretical formula of supportingstrength on the filling working face and analyzes the influences of lateral thrust frompaste material on the support of the slant working face. We hold that the lateral thrustfrom paste material is one of the reasons for higher supporting strength of supportdesign. Therefore, rapid hardening paste is an inevitable choice to reduce supportingstrength of support design and the manufacturing cost. The clamped beams model of the interaction of the filling body and theimmediate roof provides the theoretical calculating method to analyze the stability ofthe immediate roof at the early strength period of the filling body. We provide thedetermining process of filling interval through two typical calculating examples underthe conditions of medium stable roof and unstable roof. We also make a sensitivityanalysis of the major influence factors. Calculating examples point out that rapidhardening paste is favorable to increasing filling interval and improving filling miningefficiency.Simulation tests have verified the influence of goaf activation in the process ofrecycling strip coal pillars by paste filling. We put forward the evaluating method ofgoaf activation degree and make an orthogonal calculation analysis of variousinfluencing factors. The result indicates that the main influencing factor of goafactivation on subsidence is strip mining width, next to which is the strength of thefilling body.The dissertation introduces the situation of industrial application of paste fillingin Daizhuang Coal Mine. The research findings of the dissertation have been appliedin the design of paste filling mining scheme in Daizhuang Coal Mine. The result oftheoretical calculation is close to that of practical application.