Mechanism And Control Techniques Of Rockburst Disasters In Deep Mines With Thick Topsoil And Confined Water-bearing Roofs

In full-mechanized top-coal caving stopes under the deep topsoil and confined water-bearing roof,the operation work faces high mining intensity,complex geological structure and a large number of burst-inducing factors.It is very difficult to monitor and predict the dynamic disasters induced by these factors;and therefore,mining safety are seriously endangered.Based on the examples of several rockburst disasters in Juye Coalfield under the conditions of large mining depth,thick topsoil,thick coal seam and confined water-bearing roof,theoretical analysis,mechanical calculation,field test,numerical simulation and engineering analogy were used to study the rockburst mechanism in this kind of mines.Simultaneously,the corresponding methods for rockburst prevention were proposed.The main innovative results are as follows:(1)The characteristics of stress change of the confined water-bearing roof after drainage were studied.The mechanical calculation model of superposition of the abutment pressure in front of the working face and the transfer stress caused by drainage was established.The stress concentration in rockburst region was analyzed semi-quantitatively.The results indicate that the pressure-increased zone formed after drainage was an important force source for inducing rockburst disasters.In addition the results of the long-term water immersion test of coal samples in high temperatures show that the rockburst tendency index was weakened,which leads to a low bearing capacity of the surrounding rock and high risk of rockburst.It reveals the disaster-causing mechanism under the complex conditions of "high stress-strong disturbance-weakened rock mass".(2)The mechanical mechanism of rockburst disasters induced by mutual coupling factors,such as square effect of the longwall panel,stress breakdown effect and horizontal stress transfer effect,was analyzed.When the shape of the goaf behind the working face approaches a "square",the stress concentration factor and the concentrated stress reached the maximum(the force source that induces the rockburst).When the limit span of the rock layer supporting the thick topsoil were reached,the rotary motion started,and the static load applied by the topsoil was converted into dynamic load(dynamic pressure disturbance).At that time.the largest horizontal stress was transferred to the overburden,which caused the largest elastic strain energy accumulated in the overburden.If the elastic energy was released by the rotary motion of the overburden,rockburst disasters may occur.(3)The disaster-causing mechanism under complex conditions of high lateral abutment pressure,high stress in the roadway,strong disturbance of overlying strata in the stope and poor overall stability of the surrounding rock was revealed.(4)The disaster-causing mechanism of "high-energy coal body-stope dynamic loading—secondary loading of coal pillar instability" was proposed.Large elastic energy was accumulated in front of the working face due to "square effect","island effect",fold structure,lateral abutment pressure of adjacent stopes and the abutment pressure in front of the working face,which is an important cause of the rockburst.The mechanical model of the "T"-type stress transmission structure above the wide coal pillar was proposed to estimate the average stress and rockburst risk index of the coal pillar.The applied dynamic load applied by the motion of the high rock strata breaking caused by the overall instability of the coal pillar was the primary cause of the rockburst.(5)Based on the proposed mechanism,it is revealed that the key parameter for controlling the rockburst of the mine was the size of wide coal pillar.Rockburst preventing methods were proposed such as determining the reasonable advancing velocity,strengthening the pressure relief of the roadway and improving the support capability.The research results of this paper have been successfully applied to the southwestern mining area of Shandong Province,which has achieved good effects in monitoring and early warning,comprehensive prevention and control of rockburst disasters.