| Drilling for gas extraction is one of the important techniques of mine gas control and is widely used.Due to its low strength,poor stability,and external disturbance,such as mining and drilling,the orifice in the sealing section of the extraction borehole is easy to collapse and close after drilling and withdrawal,which leads to the hole cannot be sealed.In addition,the deformation and instability of the stress concentration area in the sealed section further develops the fissures around the coal body,which provides a channel for the external air to flow into the extraction pipeline,thus resulting in low concentration of gas extraction in the borehole of the soft coal seam and unsatisfactory extraction effect,which lays hidden dangers for the mine production.In this paper,considering the influence of time effect on the instability mechanism and the instability leakage mechanism of the sealing section of gas extraction borehole in soft coal seam,the new reinforcement sealing technology was proposed and the corresponding new sealing material was developed.Finally,it was applied to the field test of reinforcement and sealing of gas extraction holes in soft coal seams.The main research works are as follows:(1)The stress characteristics and instability mechanism of the surrounding coal body in the sealing section of the soft coal seam under the time effect were analyzed and solved.The grading loading creep test of soft coal samples and their perforated samples was carried out using the YYL200 electronic permanent creep tester.and the creep test parameters under the generalized Kelvin model were inversed.The variation laws of the instantaneous elastic modulus E1,the ultimate creep deformation modulus E2,and the viscosity coefficient ? with the stress level and the filling material were obtained.The results show that it was not only necessary to have a new type of sealing technology,but also a good sealing material for compression and deformation resistance,which was reasonable to solve the problems that the hole in the sealing section of the soft coal seam was easy to collapse and the stress concentration was liable to instability.(2)Based on the analysis of gas leakage in borehole of soft coal seam,a gas leakage model of borehole sealing section considering time effect was established to solve the gas leakage in borehole sealing section considering time effect.In addition,the gas extraction test platform and the leak position detection system and the borehole attenuation detection device were independently designed and built.The physical simulation test of the gas leakage in the soft coal seam was carried out,and the leakage attenuation law of the extraction holes in the soft coal seam was tested and analyzed,revealing the instability and leakage mechanism under the time effect of the borehole seal section of the soft coal seam.The results show that borehole collapse was easy to occur at 2m-5m of the borehole sealing section of the soft coal seam,and the stability of the sealing section as the main air leakage passage also determined the long-term efficient extraction of the borehole.(3)Aiming at the problem that the borehole sealing section of the soft coal seam was easy to collapse,based on the technologies of roadway spraying and the borehole reinforcing,the"concentric ring" reinforced sealing model was constructed,and the stability and air leakage characteristics of the borehole sealing section of the soft coal seam under the model time effect were analyzed.In addition,numerical simulation tests were carried out to study the optimal reinforcement radius and depth of the "concentric ring" model and the reasonable grouting pressure and time of the two grouting.The results show that the optimal reinforcement radius and depth of the "hole ring in the rock retaining wall" were 0.16m?0.18m and 0.8?1 times the roadway width,the grouting pressure should not be less than 3MPa,and the reasonable grouting time was 10min?15mim.(4)Based on the "concentric ring" model,a new reinforced sealing technology was proposed,its technical characteristics and process were studied,and a new type of sealing maternal was developed independently through a large number of ratio tests.The initial ratio design was determined by combining single factor and response surface multivariate analysis.On this basis,NDJ-5S digital viscometer and DDL600 electronic universal tester were used to test and study the fluidity and compressive strength of the new sealing maternal.and 20%?40%was selected as the best proportion of maternal gypsum.By using AutoPoreIV-9500 mercury injection instrument and DNS-200 electronic universal test,the expansion-creep characteristics of the new sealing material were studied.The results show that the compressive and deformation resistance of the maternal decreased linearly when the proportion of the material expansion agent increases.(5)In this paper,the practical application effect of the new sealing technology and material was investigated,and the field industrial test was carried out on the borehole of soft coal seam in Yuwu mining area,and the traditional effect parameters were analyzed and compared,and the test borehole was detected by using RSM-SY7 ultrasonic instrument.The results show that the new reinforced sealing technology can effectively avoid the hole collapse at the orifice of the sealing section of the borehole.The gas concentration of the test bore using the new reinforced sealing technology and materials was more than 2.5 times and 3 times that of the bore sealed with the expanded cement bag at 30 days and 60 days.The study clarified the instability mechanism of the sealing section of the soft coal seam and reveals the mechanism of instability and leakage under the time effect of the sealing section.Based on this,a new type of reinforced sealing technology was proposed and a new sealing material was developed,and the field test application was carried out in the soft coal seam mine,showing significant advantages,which is of great theoretical significance and application value for reasonably solving the instability of the sealing section of soft coal seam and improving the extraction efficiency. |
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