Study And Application On Gob-side Entry Retaining By Roof Cut And Pressure Relief In Hecaogou Coal Mine In Yanan

Based on the analysis of engineering geological conditions and the conditions of engineering mining in Hecaogou No.? coal mine in Yan'an City,the dissevtation uses theoretical analysis,laboratory experiment,numerical simulation,key technology of gob-side entry retaining by roof cut and pressure relief to study and application on gob-side entry retaining by roof cut and pressure relief in Hecaogou No.? coal mine with the shallow coal seam and thin coal seam and crushed roof.This dissevtation systematically summarizes and analyzes the difficulties and the existing causes of gob-side entry in shallow and thin coal seam and broken roof in Yan'an mining area of northern Shanxi.The stress and deformation mechanism of surrounding rock in roadway along gob-side entry are discussed in detail.This paper summarizes the characteristics and laws of deformation,fracture and instability of the gob-side entry roof with the working face mining.It was proposed to use the Constant Resistance and Large Deformation Cable(CRLD)to reinforce the roadway and pre-cracked slits using bilateral cumulative tensile blasting technology in the condition of shallow and thin coal seam and broken roof.This is the technology of gob-side entry retaining by roof cut and pressure relief in mining technology without coal pillar.Based on the gob dynamic pressure characteristics,the no pillar mining method are put forward,which deepen the research on top cut short arm beam theory.At the first,through the similar simulation experiment,the fracture characteristics and deformation regularity of roof cut and no roof cut are compared and analyzed.The results show that when the roof is not cut,the roof of the roadway and the part of the goaf are easy to form a capping triangular area.With mining of the working face and the fault of the overlying strata,the capping triangular area will gradually be shortened.During the process of rupture of the suspended rock beams,the roof of the gob-side entry will be affected by many times until the roadway is damaged.In addition,due to the largest area of the suspended rock beams in the begining of gob-side entry retaining,the overhang triangular area is responsible for the pressure of the overlying strata in the widest range,which makes the influence of the mining stresses to the roadway roof more severe.Especially during the gob-side entry retaining,the gob-side entry is easily damaged in the fracture process after the triangle area formed.The experimental result shows that the influence of the mining stresses on the stability of roadway surrounding rock can be significantly reduced by the roof cut and the influence time of mining stresses on roadway is greatly shortened.However,due to the influence of geostresses,the shear stress formed along the cutting surface is very easy to damage the roadway during the rock caving process within the scope of roof cut.Therefore,it is necessary to strengthen the roof and transform the nonlinear shear stress into a linear shear stress with constant resistance by means of CRLD cable.Based on the stress state characteristics of the roadway roof from the stress state of the original rock to the roof after gob-side entry retaining,the theoretical model of the Mohr stress circle during the gob-side entry retaining under the many times effect of mining pressure is established.And based on CRLD cable and bilateral cumulative blasting mechanics analysis,the technology of gob-side entry retailing by roof cut and pressure relief without coal pillar by vising the original roadway,the pre-spliting,parts of the rock in gob,mining pressure working and the broken rock dilatancy is put forward,and deepening the study of the theory of the short arm formed by roof cut.And then the numerical simulation analysis of the deformation and collapse characteristics of the roof rock,roof cut and no roof cut,are carried out.The results show that roof presplitting befor gob-side entry retaining,not only can significantly reduce the mining influence of goaf roof along the gob side on roadway,but also can greatly reduce subsidence of the gob-side entry.By roof cut,the tensile stress of the roadway roof can be transfered into the entity coal and the peak stress is transferred to the deeper coal.However,after the pre-spliting and during the mining stress,the roof tensile stress along the gob is still increase,therefore,it is very necessary to support the roadway roof using high preload cable during the gob-side entry retaining.In this dissevtation,the ANSYS/LS-DYNA software is applied to study the effect of boreholes spacing(400 MM,500 MM and 600 MM)and different blasting methods(interval blasting and hole blasting)on fracture patterms of rock mass.When the borehole spacing is 400 MM or 500 MM,cracks occur between two adjacent boreholes due to blasting-induced superimposition stresser exceeding tensile strength of rock mass.These cracks connect each other and a large fissile along the direction of shaped-energy is created.When the borehole spacing is 600 MM,stress waves induced by two blasting methods cannot generate more cracks between two boreholes.No matter which one method,surrounding rock in the non-converging direction do not generate new crack because its pressure is less than compressive strength of rock.Therefore,the shaped-energy blasting can control expansion direction of blasting-induced cracks.The simulation results indicate that it cannot make a continuous crack between the blasting holes when the borehole spacing is 600 MM;it can produce continuous and effective cracks when the borehole spacing is 400 MM or 500 MM.The field test show the same results:the crack of 2.4 M length are created along the radial direction,which can effectively control displacement of the roadway roof.Taking into account the construction,economic and other factors,the maximum optimal blasting plan is determine to use the interval blasting of 500 MM holes spacing.According to the numerical simulation of multi-tray bolts,under the action of multi-tray bolts on pillar,concentration stresses of gob move to gravel pillar with the gob gradually compaction.It indicates that the multi-tray bolts not only has a good effect on controlling surrounding rock,but also make the gravel pillar to help supporting the roadway short-beam structure roof.It can prompt the surrounding rock of roadway to form a stability rock structure.Multi-pallet bolts installing process encounters two phases:the first is that anchor tail anchored after collapse gangue and the second is that the roadway wall deforms during waste rock compaction process,in this process multi-tray preload automatically.Numerical simulations show that,the loading on bolt become more uniform with the increase of the number of small tray;a preload is formed between the small trays and the big trays which meet the control requirements.According to the field test of pull-out resistance of multi-tray bolts,when the number of small trays is not more than 4,multi-pallet bolts tensile strength gradually increases with the increasing in the number of small trays,and the increasing value decreases with the increasing in the number of small trays.When the number of small pallet is more than 5,tensile strength of multi-trays decrease significantly due to the small tray spacing is less than the block size of collapse gangue block;the tensile strength of no.2113 multi-trays is 8.2 t,while no.2114 multi-tray is 9.8 t.The no.2113 multi-tray bolts are applied in field.The results indicate that,the displacement of floor to roof is 0 MM after I-beam withdrawal in roadway;the displacement of two roadway walls is 0 MM where multi-trays are used,while it is 12 MM where two trays are used.Field test show that no.2113 multi-trays can control strain of surrounding rock in roadway of Heer mine.A new type of bolt is developed for controlling the strain of surrounding rock based on the test results.In case of shallow depth,thin coal seam with broken roof,large deformation occur in roof of roadway before gob-side entry retaining.So it is necessary to divide the regions according to its dangerous and put forward some effective measures.Risk assessment method,following the risk divided-zone method,are put forward to estimate the roof of roadway.Some estimation parameters are determined based on geological conditions.Support design was proposed to reinforce controlling surrounding rock in risk zone before blasting.Based on the above analysis,cutting-roof theory is applied to relief concentration stress in remain roadway.The designs are used in no.1105 tail entry of Hecaogou No.? coal mine in Yan'an City.The system technology is designed and developed and the application effect is very good.The technical principle and key technologies of the roadway along the gob are determined by theoretical results,which can achieve the goal of high productivity and high efficiency in the deep burial and deep coal seam mining in Heer coal mine.This technology recover the leaving coal pillars to help controlling coal wall splitting and relief concentration stress completely.The tension situation of mining-faces take over is also resolved.This technology make a significant economic and security sense of social benefits,bringing the economic benefits of more than 23 million RMB.It has broad application prospects and promotion significance.