Force-structure Cooperative Prevention And Control On Rockburst Fo Mining Roadway

Deep complex engineering geological tectonic environment,high engineering geological stress environment and engineering geological disturbance caused by large-scale high-intensity intensive mining make the occurrence frequency and intensity of rock burst remarkably increase.Especially the deep mine in Shaanxi-Inner Mongolia region with thick and hard roof,the layout of double(multiple)roadways in the mining face and under the wide section of coal pillar,the impact ground pressure caused by repeat mining in the remaining roadways is becoming increasingly serious.Lateral broken structure of roof in repeat mining roadway and surrounding rock stress environment of Bayangaole coal mine in Ordos as the starting points,by using the research methods of field investigation and indoor test,theoretical analysis and numerical calculation,field test and engineering practice,the main influencing factors of the surrounding rock stability of the repeat mining roadway in thick and hard rock layers was researched.The experimental simulation studies the stress characteristics of the section coal pillar under the combination of high and low thick and hard rock strata lateral different fracture positions,reveals the fracture characteristics and stress transmission mechanism of the section coal pillar lateral thick and hard roof structure in the repeat mining roadway,studies the applicability and key technical parameters of the deep hole roof directional hydraulic fracturing technology and pre-blasting technology in optimizing the lateral roof fracture structure and controlling the stress state of the section coal pillar,establishes force-structure cooperative prevention and control on rockburst for repeat mining roadway and carries out on-site effect inspection in the typical rock burst roadway.The research works of this dissertation are mainly carried out under the six aspects as follows:(1)A multi-parameter comprehensive evaluation index for the stability of repeat mining roadway is proposed and it is concluded that the main factors affecting the stability of deep repeat mining roadway in Shaanxi-Inner Mongolia region are large mining depth,thick and hard roof strata,impact tendency of coal and rock strata,width of section coal pillars and unreasonable roadway support structure.(2)With self-designed rock layer breaking rotary loading device and large-size coal and rock samples,the strain characteristics of low-level thick hard rock layer,the rock layer turning inclination angle and the stress state of the section coal pillar under four different breaking position combinations of high and low thick hard rock layers above the section coal pillar in repeat mining roadway are compared and the whole process load calculation model of the roof and the section coal pillar ultimate strength calculation model under four different breaking position combinations are established.It is concluded that under the condition of a certain section coal pillar width-height ratio,the high and low thick and hard rock strata are broken at the goaf side and the middle of the section coal pillar respectively,which is the optimal structural combination breaking scheme and the stability criterion of the section coal pillar based on the low thick and hard rock strata height is given.(3)High and low thick and hard rock strata fracture reflects the influence of lateral roof fracture structure on section coal pillar under the influence of primary and secondary mining respectively.Low thick hard rock strata control the rotation angle of high-level rock strata upward,inhibit the development of lateral fracture position to the deep,rotate downward and squeeze the short arm rock beam directly,causing the lateral stress concentration in goaf of section coal pillar and the dynamic load caused by high thick hard rock strata fracture induces the impact instability of section coal pillar in unstable equilibrium state.(4)Affect the stress distribution and structural stability of surrounding rock in repeat mining roadway are inverted trapezoidal zone and inclined block.The inverted trapezoid region has the dual functions of bearing the weight of overlying strata and transferring the stress of strata.One the one hand,the inclined block uses a masonry hinged structure to support the weight of the upper rock layer and serves as a cushion layer to absorb the impact load formed by the breaking of the overlying high level thick hard rock layer,and on the other hand is obliquely hinged with the corresponding rock layer embedded in the inverted trapezoidal structure body to provide top thrust for the inverted trapezoidal structure and control the rock layer above the low level thick hard rock layer to incline to the goaf side,thus having the dual functions of controlling the expansion of the inverted trapezoidal region and protecting the section coal pillars.(5)Optimize the structure of high and low strata fracture,increase the transmission loss of elastic energy released by high strata fracture,optimize the size of section coal pillar,cut off the energy transmission channel of bottom plate,improve the strength of roadway energy absorption and pressure support,control the stress distribution of section coal pillar,dynamically adjust the time-space combination scheme of various pressure relief measures and give the principle of energy absorption and pressure relief support coupling support and the parameter selection scheme.It is concluded that deep-hole bottom-breaking blasting combined with coal seam unloading blasting can effectively inhibit floor impact.With the core of "energy absorbing and stabilizing structure,connection breaking and consumption increasing,stress transfer and release,pressure resistance",the force-structure cooperative prevention and control on rockburst for repeat mining roadway is constructed.(6)Deep and shallow combined holes and the blasting distance is 8m,deep hole roof pre-blasting can effectively increase the density of blasting cracks and the possibility of multi-directional development,prolong the time for blasting attenuation energy to act on rocks,causing the plastic damage area to be more developed and blasting fragmentation to be more uniform,the displacement field velocity change and the effective stress peak point to be farthest from the observation point and the roof structure control effect is the best.(7)Changing the crack inclination angle ? of the semi-circular plate bending specimen and analyzing the evolution characteristics of the critical stress intensity factor curve and apparent displacement field of the crack,it was found that when 0°??<15°,the cracks are mainly type I fractures,the horizontal displacement changes rapidly,the vertical displacement changes relatively slowly and the cracks are uniformly and symmetrically distributed.When 15°???45°,the crack appears as ?/? composite fracture,but type ? fracture dominates,the change of horizontal displacement magnitude slows down while the change of vertical displacement increases.When 45°?,both K1 and K? show a downward trend,and the cracks show ?/? composite fracture.When the crack inclination angle ? is close to 45°,the in-situ stress can be fully exerted so that the crack can simultaneously bear the stretching action of the type I crack and the staggered shearing action of the type ? crack,and is especially suitable for working conditions with limited water injection pressure.(8)When the working face enters the top-broken area from the non-top-broken area or enters and exits the pre-design and construction areas,due to the inharmonious movement of the overlying roof strata structure,the discontinuous stress and energy transfer,the uneven or insufficient release of elastic variable properties accumulated in the overlying thick hard strata,cause the formation of high stress concentration in local areas,the occurrence of strong rock pressure manifestation under the action of external disturbance stress is easy to induce rock burst.At the same time,when the phenomenon of "lack of earthquake" occurs in the microseismic monitoring in these areas,it can be used as a typical prediction precursor for the occurrence of rock burst.(9)Comparing the development and location of cracks in the hole before and after fracturing,the strength and frequency of coal blasting in the roof during fracturing and the microseismic,stress changes near the auxiliary withdrawal passage before and after fracturing.It is found that compared with deep hole roof pre-blasting,deep hole roof hydraulic fracturing is superior to deep hole roof presplitting blasting technology in aspects of roof control effect,site construction efficiency,engineering quantity,restriction conditions and construction safety.Deep hole roof pre-blasting technology has the characteristics of short organization time,quick impact prevention effect and is suitable for emergency crisis relief in impact hazard areas.At the same time,deep hole roof pre-blasting technology is more suitable for the roof strata with developed primary fissures.