Abstract:The existence of the interface between soft and hard rock often makes it difficult to control the blasting effect. Studying the influence of structural plane and delayed initiation time on rock blasting characteristics can make the blasting effect more controllable. In this paper, by using the Particle Flow Code (PFC2D) and particle expansion algorithm, the double-hole delayed blasting experiments of soft-hard rock are carried out, and the results are analyzed from the perspectives of fragment gradation, micro… Show more
“…Four boundaries of the model are subjected to the compression pressure of P (P is 5 MPa), and application method of compression pressure is adopted, which is suggested by Cundall et al 32 . Figure 4 Discrete element method model of single-hole sandstone blasting 33 . …”
Section: Establishment Of Blasting Numerical Modelmentioning
confidence: 99%
“…6 , the reasonableness of the blasting method can be proved by contrast with analytical solutions of the stress with the experimental values. Figure 6 Verification of peak stress of coupled stress field 33 . …”
Section: Establishment Of Blasting Numerical Modelmentioning
confidence: 99%
“… Figure 8 Pressure load variation curve under double-hole blasting. Figure 9 Double-hole blasting numerical model of composite strata 33 . …”
By researching the distance between blasthole and interface of soft-hard rock strata, as well as the time of delay detonation, blasting effect of the rock mass will be more controllable. Firstly, validity of numerical method was authenticated from three angles: blasting coupled stress field, ratio of crushing zone radius to blasthole radius, and crack network state. Under the condition of soft-hard rock strata, numerical model of double-hole blasting was established by using PFC2D. Then delay blasting experiments were carried out under different relative positions of blasthole and interface. Ultimately, results were analyzed from three perspectives: crack network, crack quantity and rock fragment. Results show that: (1) When detonated in hard rock, if between interface and blasthole distance is greater than twice crushing zone radius, the closer blasthole is to the interface, the more obvious the “hook” phenomenon between the two blastholes is. With increasing delayed initiation time, “hook” phenomenon will weaken or even disappear. (2) Based on the crack information initiated in hard rock, the law of crack number varying with thickness of hard rock and delay time is obtained. (3) For initiation in hard rock, crack extension range is large, but less fragments are formed. The law is opposite to that initiation in structural plane and soft rock. Fragmentation area increases exponentially with increasing soft rock thickness, and exponential function is obtained.
“…Four boundaries of the model are subjected to the compression pressure of P (P is 5 MPa), and application method of compression pressure is adopted, which is suggested by Cundall et al 32 . Figure 4 Discrete element method model of single-hole sandstone blasting 33 . …”
Section: Establishment Of Blasting Numerical Modelmentioning
confidence: 99%
“…6 , the reasonableness of the blasting method can be proved by contrast with analytical solutions of the stress with the experimental values. Figure 6 Verification of peak stress of coupled stress field 33 . …”
Section: Establishment Of Blasting Numerical Modelmentioning
confidence: 99%
“… Figure 8 Pressure load variation curve under double-hole blasting. Figure 9 Double-hole blasting numerical model of composite strata 33 . …”
By researching the distance between blasthole and interface of soft-hard rock strata, as well as the time of delay detonation, blasting effect of the rock mass will be more controllable. Firstly, validity of numerical method was authenticated from three angles: blasting coupled stress field, ratio of crushing zone radius to blasthole radius, and crack network state. Under the condition of soft-hard rock strata, numerical model of double-hole blasting was established by using PFC2D. Then delay blasting experiments were carried out under different relative positions of blasthole and interface. Ultimately, results were analyzed from three perspectives: crack network, crack quantity and rock fragment. Results show that: (1) When detonated in hard rock, if between interface and blasthole distance is greater than twice crushing zone radius, the closer blasthole is to the interface, the more obvious the “hook” phenomenon between the two blastholes is. With increasing delayed initiation time, “hook” phenomenon will weaken or even disappear. (2) Based on the crack information initiated in hard rock, the law of crack number varying with thickness of hard rock and delay time is obtained. (3) For initiation in hard rock, crack extension range is large, but less fragments are formed. The law is opposite to that initiation in structural plane and soft rock. Fragmentation area increases exponentially with increasing soft rock thickness, and exponential function is obtained.
“…At the practical application level, Yuan et al 9 studied the damage mechanism of the tunnel envelope under the coupling of vertical geostress and blasting load. Cui et al [10][11][12] analyzed the change law of high geostress soft and hard rock formations under blasting load from the levels of crack state, contact coefficient, and energy magnitude. Yang et al 13 studied the influence of geostress on the degree of blast energy decay from the perspective of blast energy decay; and with the help of borehole blasting excavation method, they found that dynamic stress redistribution after explosive blast is the most important factor leading to rock damage 14 .…”
In complex high In-situ stress conditions, how to achieve ideal rock blasting effect by effective methods is often a difficult point in blasting operations. In this paper, we analyze the effect of guide holes on blasting effect by adding guide holes to the rock pre-treatment method, and carry out double-hole blasting experiments based on the blast point particle expansion method. The effect of blasthole spacing and ground stress on blasting effect is investigated at macroscopic crack effect, microscopic particle contact and stress response level. The study shows that: (i) The crack penetration effect can be enhanced by setting guide holes between blastholes, and the penetration effect is more obvious when the distance between blasthole and guide holes is less than 2.5 times the radius of the crushing zone. (ii) At the contact force chain level, when the distance between blasthole and guide hole is less than 2.0 times the radius of crushing zone, the pressure stress perpendicular to the direction of blasthole linkage inhibits the development of crack, and the pull stress parallel to the direction of blasthole linkage promotes the development of crack; at the contact number level, the distance between blasthole and guide hole The main force direction is perpendicular to the blasthole line direction when the contact number level is less than 2.0 times the radius of the crushing zone. (iii) With the increase of distance between blasthole and guide hole, the inhibition of crack by stress in the vertical direction is weakened, and the main force direction is parallel to the blasthole line direction.
“…Regarding other engineering levels, Yuan et al 23 provided a methodological basis for increasing the mining rate of uranium ore by using blasting and fracturing techniques to expand the tiny cracks in the rock body and increase the permeability of uranium-bearing sandstone. Cui et al [24][25][26] took the blasting of weakly interbedded rock as a research point. They analyzed the influence of weakly interbedded rock on the blasting effect regarding crack effect, stress field, energy field, etc.…”
In engineering, blasting is often used to achieve engineering purposes. Still, more studies are limited to a single rock layer, and there are few details on complex rock layers, such as interbedded rock bodies. This paper analyses the effects of the blasting environment, layer thickness, and inclination angle on the blasting effect from the levels of reflected stress, cracking state, and contact resultant force with the help of the particle expansion method. It is found that: (i) The blasting environment and layer thickness greatly influence the blasting effect, while the inclination angle has a minor influence. (ii) When the layer thickness in a hard rock environment is less than seven times the radius of the crushing zone, the reflective stress near the contact surface increases with the layer thickness, conversely, it decreases. (iii) For hard rock environments with layer thicknesses up to 3 times the radius of the crushing zone, the number of cracks increases with layer thickness at a rate of 68% per meter, conversely, it decreases at a rate of 6.5% per meter. For soft rock environments with layer thicknesses up to 1 times the radius of the crushing zone, the number of cracks decreases at a rate of 112% per meter with layer thickness. It increases at a rate of 10% per meter for layers between 1 and 2 times the radius of the crushing zone. (iv) The average contact resultantforce increases at a rate of 15.4% per meter when the layer thickness gradually increases to 10 times the radius of the crushing zone for hard rock environments and decreases at a rate of 51.7% per meter when the layer thickness increases to 1.5 times the radius of the crushing zone for soft rock environments, and converges if the layer thicknesses continue to increase for both soft rock and hard rock environments.
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