Basci Experimental Study On Long-Term Stability Of Deep Strip Coal Pillar

As time goes on, some strip pillars will be unstable and collapse in the future then they are steay at formerly, those pillars become potential disasters while development of other industrial in old mining areas.At the same time, in order to extend the mine life, some mines have to consider to exploitate the former pillars.Deep pillar timeliness is more obvious, study the long-term stability of deep coal pilla has a positive role r to reduce disasters caused by coal pillar losing stability and can provide a scientific basis to reexploitate coal resources. A more systematic basic research on the long-term stability of deep strip coal pillar affected with time is carried out by the use of laboratory testing, field measurement, numerical simulation and theoretical analysis methods in this paper. The main study achievements were as follows.(1) The long-term of strip coal pillar stability manifests at the creep of pillar strength and development & stabilination long-term of pillar & overlay stratum. Some factors are analyzed as strip coal pillar of geological conditions, coal pillar own conditions, time and water influencing on long-term stability. The stope spatial structure models of small and large strip mining width are put forward based on mine pressure theory. The theoretical strength of strip pillar should include the scale effect, lateral constraint effect and time effect.(2) Unaxial compressed tests of several typical rocks'classⅠand classⅡcurves are carried out, and the formation mechanism and access method and production conditions of classⅡcurve are analyzed. Dimension-form effect for compressive strength of coal sample is experimental studied and the relation between UCS and coal mass strength in scene.(3) Creep tests are carried out and coal creep failure characteristics and mechanical parameters and constitutive model are analyzed. The existence of the micro-failure and brittle mutation deformation is proved in the creep process of coal through exact creep experiment. The influence on coal creep characteristics of water immersion is studied through contrast creep tests between natural and saturated water coal samples. The concepts of absolute long-term strength and relative long-term strength are cleared and the influence on coal long-term strength is studied through short-term and relative long-term creep tests. The formula of rock long-term strength is put forward asσT=σ∞+A exp(-Bt), then the theoretical long-term strength of coal tested is ascertained as 8.2282MPa.(4) Strip pillar long-term stability of Daizhaung Coal Mine performance is analyzed though numerical experiment using LS-DYNA and FLAC3D combination of laboratory test results and comparing the results of field measurement. The results show that pillar state is still undergoing changes after a long time of the end of mining activities, but these changes will become increasingly smaller. After 15-16months of mining, the coal pillar chang into long-time stable state. (5) The long-term monitoring of coal pillar stability is established, pillar long-term stability performances are monitored in Daizhaung Coal Mine and Tangkou Coal Mine and those evolution laws are analyzed. Based on actual observation, the strip pillar in Daizhaung Coal Mine is divided into elastic core zone, plastic failure zone and completely failure zone and the scope of each zone is determined. The strengths of different parts of the coal pillar are determined through on-site observations. The long-term strength of pillar in Daizhaung Coal Mine is determined as 29.5MPa combination of field observations and laboratory test results and pillar long-term stability performance is analyzed. Based on actual observation, scope of each zone and position of peak pressure and strength from Tangkou Coal Mine strip pillar and lateral incidence of mining are studyed and pillar long-term stability performance is analyzed.(6) Actual observation also shows that the transverse deformation in deep pillar of deep mine is non-continuous, step-type, mutant type. Rocks'flexibility, brittle and impact resistance also will be demonstrated even more prominent though the rocks perform plasticity since bearing more pressure in deep mine that perform elasticity and brittle in shallow mine.