Investigation On Principle And Application Of Directional Rock Breaking By Instantaneous Expansion

Major national strategies such as underground resource mining,national defense engineering,tunnel excavation,water conservancy and hydropower engineering all require directional rock breaking technology.Therefore,rock directional fracture is a common scientific problem in the field of rock mechanics.Directional rock breaking is the key common technology to solve this problem.To this end,a new and original directional rock breaking technology,called instantaneous expander with a single fracture surface,has been developed.This technology uses non-explosive new materials with solid wastes such as coal gangue and straw as the main raw materials to instantly generate a single fracture surface,realizing the green manufacturing and utilization of waste resources,and turning waste into treasure.The crack propagation mechanism and engineering response mechanism of instantaneous expander with a single fracture surface are revealed by theoretical analysis,laboratory experiments,numerical simulations and field tests.The following main conclusions are obtained:(1)Instantaneous expander with a single fracture surface transforms the three-dimensional fracture of conventional blasting into two-dimensional directional fracture.The crack propagation evolves in a "point-line-surface" type,that is,"point-type force,line-type crack initiation,and surface-type forming".Based on the effective stress principle,the directional crack initiation criterion is established.In the state of hydrostatic pressure,the crack initiation pressure does not change with the change of the kerf angle.In the state of non-hydrostatic pressure,the crack initiation pressure changes as a cosine function with the kerf angle.According to the space shape of flat ellipsoid crack,the directional crack propagation criterion is established under the dual action of in-situ stress and the gas pressure.The mechanism of meso-directional fracture at the crack tip under the multi-field coupling of in-situ stress field,gas pressure field and skeleton stress field is analyzed,and the pore gas pressure required for the mesoscopic fracture of skeleton particle body and skeleton particle is obtained.(2)Multi-crack cracking and single-crack slitting experiments were carried out with single-hole and double-hole concrete samples,and single-crack slitting experiments were carried out with plexiglass transparent material.In these experiments,high-speed cameras were used to capture the dynamic evolution of cracks;ultra-dynamic signal testers were used to reveal the law of stress distribution in the process of crack propagation;changes in wave velocity were used to quantitatively characterize the damage in both the cutting and non-cutting directions.When instantaneous expander with a single fracture surface fracturing concrete,the stress change in the cutting direction is divided into four stages: unexcited stage,compressive stress stage,tensile stress stage,stable stage;the stress change in the vertical cutting direction has only three stages: unexcited stage,compressive stress stage,stable stage.The directional rock-breaking mechanism is that the tensile stress is concentrated in the cutting direction,and the non-cutting direction is compressed,so the fracture is formed by tensioning under the action of high-energy gas.The damage caused by instantaneous expander with a single fracture surface presents the characteristics of "high in the middle and low on both sides".The damage value at and near the directional crack is larger,and the damage at the rest is smaller.(3)Based on the heterogeneity equation,the stress field equation,the damage constitutive equation of the meso-element and the loading equation in the hole,the multi-field coupling simulation software COMSOL is used to simulate the single-hole single-crack and single-hole multi-crack cutting,and obtain the variation law of parameters such as stress,strain,displacement,and damage variables in the direction of energy accumulation and non-energy accumulation.When instantaneous expander with a single fracture surface breaks rock,the damage in the cutting direction is 7.92 times that in the non-cutting direction,the stress in the cutting direction is 2.16-3.71 times that in the non-cutting direction,the displacement in the cutting direction is 1.56 times that in the non-cutting direction,and the strain in the cutting direction is 8 times that in the non-cutting direction.The crack propagation law and stress-strain-damage law by double-hole explosive blasting,shaped blasting and instantaneous expander with a single fracture surface are comparatively studied.When instantaneous expander with a single fracture surface breaks the rock,the damage degree is smaller than that of the shaped charge blasting and conventional blasting,so its directional rock breaking effect is the best.In the process of crack initiation and propagation,the superposition of tensile stress between the holes gradually increases,and the stress concentration decreases after the crack is penetrated.(4)For the self-formed roadway without coal pillars by roof cutting,the mechanism of stress release and stress compensation synergistically controlling the deformation of surrounding rock is revealed.The cutting rate of the instantaneous expander is 9-11% higher than that of the explosive,and its power is greater.After directional roof cutting,the collapsed gangue fills the goaf by utilizing the dilatancy of crushed rocks to form a roadway and control the movement of the overlying strata.The equivalent direct roof above the roadway forms a "cut roof short arm beam" structure,and the basic roof forms a "hinged rock beam" structure.Compared with the traditional mining method,the roof cutting by instantaneous expander with a single fracture surface can significantly reduce the mine pressure and make the roadway in a low stress environment.The average working resistance of the hydraulic support on the cutting side is 32% lower than that on the non-cutting side.At present,the directional roof cutting technology of instantaneous expander with a single fracture surface has been successfully applied in 7 mines.The applied roof types include shallow buried hard roof,composite roof and deep hard roof.(5)Comparative tests were carried out on three methods of roadway excavation:conventional explosive blasting,explosive shaped charge blasting and instantaneous expander.Compared with conventional explosive blasting and shaped charge blasting,the instantaneous expander has significant advantages.The over / under excavation area decreased by 64% and 17%,the maximum over / under excavation depth of the roof decreased by 74% and 34%,the maximum over / under excavation depth of the tunnel wall decreased by 62% and 22%,and the half mark rate of peripheral eyes increased by 80% and 9% respectively.The peripheral eye adopts instantaneous expander to change the energy generated from free divergence to orientation,which can accurately control the crack propagation direction,and form a smooth contour surface.The average excavation disturbance zone of the instantaneous expander is 1.7m,which is 11% less than that of explosive shaped charge blasting and 26% less than that of conventional blasting.Therefore,the instantaneous expander reduces the damage disturbance range of surrounding rock and improves the stability of roadway.The dissertation has 176 figures,36 tables,and 275 references.