Study On Blasting Damage And Crack Propagation Of Eccentric Uncoupled Charge

Smooth blasting and pre-splitting blasting are the most widely used controlled blasting techniques in stone tunnel and roadbed excavation projects.Radial uncoupled charge structure is usually used to weaken the rupture and damage of surrounding rock caused by strong impact of explosive explosion.Most of the existing uncoupled charge blasting theories are based on the hypothesis that the cartridge center coincides with the hole center.However,in actual blasting engineering,due to the gravity effect,it is difficult to ensure that the charge center coincides with the axis of the borehole in site construction,which eccentric uncoupled charge is a common phenomenon.Eccentric uncoupled charge blasting will cause different degrees of damage and cracks to the blasted medium in different directions of the borehole wall,resulting in blasting over-underbreak or affecting the stability of the reserved rock mass.Although many achievements have been made in the study of blasting with eccentric uncoupled charge,it is still unclear how the eccentricity degree of charge causes fracture and damage to the rock mass around the borehole wall,and there is no quantitative method to express it.Therefore,the research on this problem has certain theoretical research value and engineering reference significance for correctly understanding the effect of eccentric charge structure in uncoupled charge blasting such as smooth blasting or pre-splitting blasting.Based on the analysis and summary of the existing blasting theory of eccentric uncoupled charge structure,the eccentric uncoupled coefficient is defined to describe the different eccentricity degree of cartridge in the borehole.By means of numerical simulation technology and control model test,the damage range and distribution rule of rock mass near the borehole wall caused by explosion of cartridge under different eccentricity are studied.At the same time,numerical simulation method is used to establish the blasting numerical model of fully eccentric uncoupled charge structure with different hole spacing,and to study the crack propagation law of rock mass under the action of stress wave.The conclusions are as follows:Firstly,in the single-hole three-dimensional numerical simulation experiment,with the increase of the eccentricity coefficient of the cartridge,the damage scope of the blasting stress wave on the eccentric side of rock mass gradually increases,the crushing zone slowly increases,and the fracture zone decreases linearly.The damage zone of non-eccentric rock mass decreases gradually,the fracture zone increases linearly,and the comminution zone decreases rapidly or even disappears.When the charge is completely eccentric,the crushing zone of the rock mass on the eccentric side is about twice as large as that of the centralcharge structure.Secondly,through the model test,it is known that the damage degree decreases "S" with the increase of the distance from the explosive source,which indicates that the explosive shock wave consumes a lot of energy when crushing rock near the borehole wall.Under the condition of completely eccentric uncoupled charge,the damage range of eccentric side is about 1.25 times that of non-eccentric side,which is similar to the results of numerical simulation.Finally,in the numerical simulation study of double-hole eccentric uncoupled charge blasting,the average radius of crack propagation of rock mass on the contact side of cartridge and borehole wall is larger than that on the uncoupled side,which indicates that the blasting of eccentric charge structure has obvious stress eccentricity effect on borehole wall.However,the average radius of the fissure zone between two adjacent holes is almost the same after blasting,which indicates that the holes on rock mass have no guiding effect on the blast stress wave.