| Directional blasting construction method has become an important driving method for underground roadway and tunnel construction because of its advantages of good forming and high speed.Because the underground roadway is always in a state of high stress,the damage control of retained rock mass by blasting has become a problem that needs to be paid attention to.Directional fracture blasting with slit charge is one of the most widely used means,and the evolution of its blasting damage is the research focus of controlling directional fracture effect and surrounding rock damage.Previous people have done a lot of research on the blasting mechanism of slit charge from the angle of ripple relation and constitutive relation,but the research based on the angle of damage distribution and evolution is relatively few.In this thesis,the experimental study on the damage and fracture evolution law of rock caused by directional fracture blasting with slit charge is carried out.In this thesis,the different factors affecting the blasting effect and damage and fracture evolution of slotted charge are studied by means of macroscopic crack analysis after blasting,hyper dynamic strain analysis,two-dimensional damage degree analysis of charge segment,three-dimensional damage degree analysis of CT scanning reconstruction model,dynamic response analysis of rock medium SHPB with different distances from the blasthole and fractal calculation of fragmentation.The evolution mechanism of explosive damage of slit charge was experimentally studied from the aspects of slit tube material,slit direction and slit width,radial decoupling coefficient and uncoupling medium in uncoupled charge structure,and different distances from the blasthole.At the same time,based on the discontinuous deformation analysis(DDA)method,the rock-breaking mechanism,damage and fracture evolution of slit charge and ordinary charge were compared and simulated.The main contents and achievements of this thesis are as follows:1.The damage and fracture evolution of rock under the blasting load of slit charge that is coupled and uncoupled was tested,and comprehensive analysis was carried out by means of industrial CT scanning reconstruction,strain monitoring and fractal dimension calculation.According to the changing rules of the peak strain ratio of slit direction to vertical slit direction,the ratio of incident compressive strain to reflected tensile strain,and the ratio of two-dimensional and three-dimensional damage degree,the influences of slit tube material,slit direction,slit width,radial uncoupling coefficient,uncoupling medium and other factors on the energy accumulation and directional fracture damage effect of slit charge are systematically revealed.(1)The blasting effect of slit charge is positively correlated with the elastic modulus of slit pipe material.Under certain conditions of slit tube thickness,slit width and slit length,the energy gathering and directional fracture effect of slit tube become stronger with the increase of elastic modulus of slit tube material.It shows that the ratio of the two-dimensional and three-dimensional damage degree of the slit charge to the vertical slit direction gradually increases.The more explosive energy of the slit charge is used to destroy the rock medium in the slit direction to do work,and the higher the peak strain,the higher the damage degree of the rock medium.(2)The existence of slits can indeed realize directional fracture blasting of rocks.The explosive energy of the unidirectional slit charge is preferentially emitted from the slit direction,which causes the rock medium to be damaged.At the same time,due to the explosive gas and other explosive products being emitted along the slit direction,the slit pipe is pushed in the reverse direction along the slit,which causes the surrounding rock medium in the reverse direction of the slit to be damaged.The failure mode is similar to180 degrees double slit failure,but the bilateral failure is uneven.When the slit angle is90 degrees,the slit explosive charge not only makes directional fracture blasting,but also damages the surrounding rock media in the opposite direction of the parting line in the slit angle,and the damage effect is herringbone.With the increase of slit angle of slit charge,the damage in slit direction increases.The damage on one side of the protected rock medium is reduced,and when the slit angle is 180,almost no damage occurs in the vertical slit direction.(3)When the material,thickness and slit length of slit tube are constant,there is an optimal threshold for slit width.The relative optimum width is related to the material of slit tube and the thickness of tube wall.When the slit tube is made of steel,the outer diameter is 6mm,the inner diameter is 4mm,the wall thickness is 1mm,the slit length is the same,and the slit width is about 1 mm,the ratio of damage degree(2D,3D)of rock along the kerf direction to damage degree in the vertical kerf direction is the largest,and the kerf pipe has the best energy gathering effect and directional fracture ability.(4)The radial decoupling coefficient of slit charge and the directional fracture effect of slit charge have a quasi-normal distribution relationship,and the radial decoupling coefficient has the best threshold.When the decoupling coefficient is 1.67,the ratio of the damage degree in the slit direction(2D,3D)to the damage degree in the vertical slit direction is the largest,the slit tube has the best energy gathering effect and the directional fracture blasting effect is the best.At the same time,the damage to the protected rock mass is minimal.(5)When the uncoupled medium is water,the slit charge has the best energygathering effect,and the ratio of the damage degree in the slit direction to the damage degree in the vertical slit direction(2D and 3D)is the highest.The air decoupling blasting effect is second,while the stemming decoupling blasting effect is poor.2.In order to study the distribution and development law of different damage areas of rock media in the slit direction and non-slit direction under the explosive load of slit charge,the SHPB method was adopted to carry out dynamic mechanical response tests on the damage areas of rock media with different distances from the blasthole in the slit direction and the vertical slit direction.According to the ratio of dynamic yield strength of rock to original rock strength as the method of judging damage degree,the damage distribution and evolution law of rock media with different distances from the blast hole under the explosive load of slit charge is revealed by means of fractal dimension.(1)The dynamic strength of rock is defined as the damage degree of rock,and it is calculated that the damage degree of rock in the slit direction is greater than that in the direction perpendicular to the slit,and the rock medium which is 150 mm away from the blasthole in the direction perpendicular to the slit is hardly affected by explosion load.(2)The damage degree of rock in the slit direction and perpendicular to the slit direction decreases exponentially with the increase of the distance from the blasthole,and the attenuation index of the damage degree in the slit direction(﹣0.3876)significantly larger than that in the perpendicular direction(﹣0.8953).(3)The fragmentation distribution of rock samples under impact load shows good statistical self-similarity.With the distance from the core to the blast hole,the fractal dimension of the damaged samples increases,and the fractal dimension of the samples perpendicular to the slit direction with the same distance(2.0205～2.2196)is larger than that of the samples along the slit direction(1.3948～2.0159).3.Based on the discontinuous deformation analysis(DDA)method,a numerical model for simulating the development of rock damage and fracture under explosion load is developed.The evolution process of rock fracture damage under explosion load of slit charge and ordinary charge is simulated,and the mechanism and evolution law of fracture damage of slit charge are revealed.(1)Different from common blasting simulation methods(such as finite element method,etc.),DDA method can directly simulate the whole evolution process of crack development and expansion,which is very suitable for the analysis of explosion problems.(2)The explosion stress wave acts on the slit to produce the tensile stress concentration area,and the difference between the slit tube material and the rock material leads to the obvious attenuation of the stress wave transmitted into the rock at the nonslit part of the slit tube,which is the internal mechanism that the slit charge can realize directional blasting.(3)Under the explosive load of slit charge,relatively straight tensile cracks are mainly produced at the slit tip,and their shapes are relatively symmetrical.However,under the explosion load of ordinary explosive charge,when the peak value of the explosion stress wave is larger or the rock strength is smaller,dense crushing zones will be generated near the blasthole,which will limit the development of cracks.(4)The peak pressure and duration of explosion stress wave have obvious influence on rock fracture under the explosive load of slit charge.The longer the duration,the longer the cracks at the slit;the peak pressure should be reasonably selected to reduce the fracture zone while ensuring the crack length. |
PDF Full Text Request