Research On Crack Propagation In Water Hole Smooth Blasting

The smooth blasting technology requires the blasting of the smooth blasting layer,the formation of through cracks between the surrounding holes,while reducing the damage of the surrounding rock and protecting the stability of the surrounding rock.However,with the continuous development of smooth blasting technology,the requirements for smooth blasting effect are higher and higher,and the selection of smooth blasting parameters will also directly affect the engineering quality.In order to solve the problems of incomplete rock fragmentation,over-excavation and under-excavation of surrounding rocks encountered in the actual smooth blasting project,and with the promotion of high-power anti-water gel explosive and emulsion explosive,it is particularly important to study the influence of smooth blasting parameters on smooth blasting of water holes and crack propagation.In order to further explore the crack propagation characteristics of water hole smooth blasting rock mass,this paper uses numerical simulation method to explore the crack propagation process of smooth blasting.Firstly,the radial water non-coupling coefficient is determined by the rock damage range and the peak pressure of the blasting hole wall,and determine the charging method for subsequent modeling;then the rock failure criterion is determined by numerical analysis,and the dynamic evolution process of smooth blasting crack coalescence of water hole is obtained by numerical simulation;finally,the influence of smooth blasting parameters on crack propagation is analyzed by changing the hole distance and the thickness of the smooth blasting layer.The main research contents and conclusions are as follows:(1)Through the analysis and comparison of the rock damage range and the peak pressure of the blasting hole wall after the blasting of the radial water non-coupled charge and the axial water non-coupled charge,it is concluded that when the radial water non-coupling coefficient is 2.5,it can not only ensure that the peak pressure of borehole wall is less than the dynamic compressive strength of rock,which is not enough to cause the borehole wall to be crushed and meet the requirements of smooth blasting,but also produce a smaller damage range.Compared with the axial water coupling charge,the damage range after blasting is more uniform,and the smooth blasting effect is the best.(2)The orthogonal combination of the three failure criteria of the minimum hydrostatic pressure,the minimum principal strain and the maximum shear strain was simulated by numerical simulation to obtain a more reasonable joint effect.The research shows that when the minimum hydrostatic pressure,minimum principal strain and maximum shear strain failure criteria are set at the same time,the joint effect between the holes is the best,and each failure criterion is used to control the tensile,compression and shear failure respectively.After the explosion of explosives,the shock wave acts on the blasting hole wall,and the rock within a small range around the blasting hole wall is completely compressed.After that,due to the combined action of compression and shear,the crushing zone is formed,and the rock outside the crushing zone is subjected to tensile failure and cracks are generated.(3)After selecting a reasonable failure criterion to obtain a crack that is more consistent with the actual situation,and the corresponding research on the process of porous crack formation under the radial water decoupling charge of smooth blasting is carried out by using this failure criterion.The crack formation of porous smooth blasting is the result of the dynamic evolution of cracks.The main stages are : "the formation of the crushing zone near the hole wall-the initial radial cracks outside the crushing zone begin to form the fracture zone-the continuous independent extension of each hole diameter to the cracks-the successive penetration of cracks between holes-the secondary crack extension and the crack near the free surface-crack arrest " It is also considered that the fracture coalescence between boreholes is caused by the combined action of tangential tensile stress,radial tensile stress and explosive gas,in which the radial tensile stress and tangential tensile stress generated during the propagation of stress wave play a decisive role in fracture coalescence.(4)By changing the thickness of smooth blasting layer,the influence of different thickness of smooth blasting layer on crack propagation is analyzed and studied.The results show that with the increase of the thickness of smooth blasting layer,the cracks in rock along the free surface are less and less.By changing the borehole spacing,the influence of different borehole spacing on the crack propagation between boreholes is analyzed.The results show that with the increase of hole spacing,the cracks between adjacent holes are less and less.