| Gob side entry retaining by roof cutting is a technology without pillar,which can realize systematic prevention and control from the whole to the local and provides a new idea for the safety prevention and control of coal burst in deep coal mine.From the perspectives of pressure relief by roof cutting and absorbing energy by supporting materials,this thesis takes the Guotun Coal Mine of Shandong Energy Group as the engineering background and is systematically studied by the combination of theoretical analysis,numerical simulation,laboratory test and industrial test.Based on theoretical analysis and numerical simulation,the mechanism of coalburst prevention and the evolution law of stress and energy of surrounding rock of gob side entry retaining by roof cutting is systematically studied,and the effect of pressure relief and energy reduction is verified.The true triaxial impact dynamic test of anchored rock sample with new energy absorbing support material is carried out,and the impact resistance characteristics and surrounding rock control effect of new energy absorbing support material are verified.The design method of strength and energy support and comprehensive evaluation system of gob side entry retaining by roof cutting without pillar are established and successfully applied in Guotun coal mine(the maximum buried depth is 890 m).The main research contents are as follows:(1)Through the numerical simulation,the stress and energy of surrounding rock in the whole process of gob side entry retaining and reused is quantitatively analyzed between gob side entry retaining by small coal pillar and gob side entry retaining by roof cutting,and the effect of pressure relief and energy reduction using gob side entry retaining by roof cutting is verified.The results show that compared with the technology of gob side entry retaining by small coal pillar,the stress of surrounding rock of gob side entry retaining by roof cutting at the same position of gob side entry is significantly reduced,and the peak value of lateral abutment pressure is transferred to the deeper location;Through the comparative analysis of the accumulated energy in five key areas of the surrounding rock of the gob side entry under the two mining technologies,gob side entry retaining by roof cutting has no energy accumulation in the area of coal pillar,and the other four areas of accumulated energy is reduced.Thus,the overall accumulated energy of surrounding rock gob side entry retaining by roof cutting is greatly reduced.(2)The effect of pressure relief and energy reduction using the technology of gob side entry retaining by roof cutting is analyzed and calculated by Mohr Coulomb strength criterion and theoretical analysis,revealing the mechanism of coalburst prevention and control.The influence of the cantilever length of the low-level roof on the bending moment energy is analyzed.At the same time,the calculation formula of the maximum bending moment energy of the high-level roof of gob side entry by roof cutting is established,and the influence of the key factors of the support strength of coal rib,roof support and the broken and expanded gangue support strength on the bending moment energy of the high-level roof is discussed.The results show that reducing the cantilever length of the low-level roof can reduce the accumulated bending moment energy of the low-level roof,and the support strength of broken and expanded gangue plays a leading role in the energy control effect of the high-level roof,which effectively reduces the risk of coalburst.(3)The true triaxial impact dynamic test of rock sample anchored by new energy absorbing support material is carried out,the mechanical properties,failure characteristics,acoustic emission parameters and force of support materials under the same dynamic pressure disturbance conditions of unsupported rock samples and anchored rock samples of new energy absorbing support materials are studied,and the impact resistance characteristics and surrounding rock control effect of new energy absorbing support material are verified.The results show that compared with the rock sample without support,the peak strength is greatly improved,the failure time is later,the acoustic emission count and energy parameters are reduced,the mass of ejection debris is reduced and the distance is shorter,the force of the new absorbing energy support material is significantly increased,and the surrounding rock control effect under the condition of impact disturbance is effectively improved.(4)The strength support design of gob side entry retaining by roof cutting comprehensively considers the short arm beam theory,the minimum support strength criterion of solid coal rib and the design criterion of broken and expanded gangue retaining strength;The energy support design of gob side entry retaining by roof cutting comprehensively considers the micro-seismic source energy,accumulated energy of surrounding rock,minimum failure energy of surrounding rock and absorbing energy of support materials,and establishes the energy design criteria;The support design method of strength and energy of gob side entry retaining by roof cutting is established,which meets both the strength design criteria and energy design criteria.Taking Guotun coal mine as the engineering background,the reasonable support parameters of roof,solid coal rib and gangue rib are designed.According to the support design method of strength and energy of gob side entry retaining by roof cutting,the effectiveness of energy absorption and coalburst control of the support design parameters is checked.(5)The comprehensive evaluation system of balanced mining using the technology of gob side entry retaining by roof cutting was established in deep mine,and the field engineering application of deep mine was carried out.By using the comprehensive monitoring system,the evaluation method of mine pressure and energy parameters,the characteristics of deformation,stress and energy parameters of surrounding rock between gob side entry retaining by small coal pillar and gob side entry retaining by roof cutting are compared and analyzed.Compared with the gob side entry retaining with small coal pillar,the micro-seismic frequency in the influence area of gob side entry retaining by roof cutting was 82 times,which was reduced by 30.51%,the maximum energy was4.90×10~3J,which was reduced by 62.33%,the total energy was 3.59×10~4J,which was reduced by 47.80%and there was no large energy event above 1×10~4J.Through field industrial test,it is verified that the technology of gob side entry retaining by roof cutting without pillars is effective in reducing the risk of coalburst disaster. |
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