| In recent years,rockbursts have occurred frequently in the mining roadway of the ultra-thick coal seam in China,it was urgent to theoretically reveal the mechanism of rockburst in the mining roadway of ultra-thick coal seam and put forward prevention and control techniques,to provide a theoretical basis and technical support for the prevention and control of rockburst in ultra-thick coal seam.This thesis takes the fully mechanized top coal caving face of 10 m ultra-thick coal seam in the Longjiapu coal mine in Jilin Province as the engineering background,using the research methods of theoretical analysis,numerical simulation,laboratory test,and field test,taking energy as the mainline,the mechanism of rockburst in mining roadway of the typical ultrathick coal seam was systematically studied from the whole process of inoculation,release,transmission,and appearance of impact energy,on this basis,a multidimensional rockburst prevention and control technology system was constructed and applied in engineering from three aspects of “weakening the impact energy source,destroying the impact energy transmission path and protecting the appearance position of impact energy”.The main research results are as follows:(1)The mechanism of rockburst in the mining roadway of the typical ultrathick coal seam was revealed.It was found that:(1)The ultra-thick coal seam has good energy storage conditions,under the condition of large burial depth,the combined action of origin stress and abutment pressure leads to the storage of a large amount of elastic strain energy in the coal seam,while the thick layer suspended roof above the goaf stores a large amount of bending strain energy,both of them continuously accumulate and release energy under the influence of mining,forming an impact energy source;(2)Under the action of high stress,the compacted coal body has good energy transfer performance so that most of the impact energy can be transferred to the vicinity of the roadway;(3)Under the influence of high stress and microseismic(MS)events,the surrounding rock of the roadway continues to creep deformation,and the support system is in a critical failure state because it can not adapt to the surrounding rock deformation.When the impact energy acts on the roadway,the support system breaks,and the rock burst occurs.(2)The rockburst prevention mechanism of pressure relief by roof cutting was studied.Through mechanical analysis,the mathematical relationship between the abutment pressure and the roof cutting height,the mathematical relationship between the maximum tensile stress of the hanging rock beam and the hanging length were deduced respectively,and the stress characteristics of the coal body and the rear hanging roof of the working face under the support of gangue were analyzed;Through numerical simulation,the energy distribution characteristics of the coal body and the rear hanging roof under the influence of pressure relief by roof cutting were studied.The study found that:(1)After pressure relief by roof cutting,the crushed gangue can limit the subsidence movement of the key strata above the goaf,weaken the abutment pressure of the coal body and reduce the maximum tensile stress in the suspended rock beam,so as to weaken the energy accumulation level in the coal body and the tension of the roof;(2)After roof cutting and pressure relief,the elastic strain energy stored in the coal body and the rear hanging roof of the working face was greatly reduced,which indicated that the roof cutting and pressure relief effectively weakens the two main impact energy sources of the working face of the ultra-thick coal seam,and can prevent the occurrence of rockburst from the root.(3)Based on the “creep-impact” test,the impact failure characteristics of roadway surrounding rock under the influence of pressure relief by roof cutting were studied,the main contents include two aspects:(1)The “creep-impact” tests under different creep loads were carried out to explore the influence of creep load reduction on impact failure of roadway surrounding rock after pressure relief by roof cutting.The results show that: Under lateral constraints,both plastic failure,and intact coal samples have a good bearing capacity,under the same impact condition,the higher the creep load,the more prone to impact failure;(2)The impact test of coal sample under the influence of pre-splitting plane angle was carried out to explore the influence of pre splitting plane angle on impact energy transmission.The results show that: The existence of pre-splitting surface can effectively reduce the amplitude and energy of stress wave,and the degree of reduction increased with the decrease of the angle between the incident wave direction and the pre-splitting surface.(4)The deformation and failure characteristics of coal samples strengthened by NPR cable and ordinary cable under “creep-impact” load were explored respectively,and the coordinated control technology of large impact deformation of mining roadway based on NPR cable was proposed.The results show that: The strain increment of NPR cable reinforced coal sample in the process of impact and creep is less than that of ordinary cable reinforced coal sample,the final fracture form is mainly single tension fracture,and there without cable fracture and rock mass throwing;The final fracture form of ordinary cable reinforced sample was a tension-shear composite fracture,the cable fracture and rock mass throwing at the moment of coal sample fracture.(5)Based on the principle and effect of pressure relief by roof cutting,puts forward the whole stope step pressure relief technology,which is used as the first-class pressure relief by open-off cut,double gateway,and the retracement channel roof cutting,and the pre-splitting high-level rock stratum by double gateway deep hole blasting as the second-class pressure relief technology;Based on the impact resistance characteristics of surrounding rock anchored by NPR cable,the support of “full section NPR cable + shrinkable O-shaped” was proposed to resist the creep load of surrounding rock;The support of "full section NPR cable + shrinkable O-shaped +energy absorption support" was adopted to resist the “creep + impact” a load of surrounding rock during mining.(6)Combined with the whole process of rockburst energy gestation,release,transmission,and occurrences,this thesis puts forward the idea of multi-dimensional rockburst prevention and control by “weakening the impact energy source + destroying the impact energy transmission path + protecting the impact energy occurrences position”.In terms of weakening the impact energy source,it was proposed to reduce the energy stored in the coal body and roof using the support effect of crushed gangue by the whole stope step pressure relief technology;In terms of destroying the impact energy transmission path,it was proposed to increase the energy loss in the process of stress wave transmission through the roof cutting pre-crack surface;In terms of protecting the appearance position of impact energy,the multi-level energy absorption support technology was put forward by using “full section NPR cable + shrinkable Oshaped + energy absorption support”.On this basis,the multi-dimensional rockburst prevention and control technology system of mining roadway in ultra-thick coal seam was established,and the design method and process flow were determined.The results have been successfully applied in the Longjiapu coal mine and achieved good rockburst prevention and control effect. |
