Model experiment on dynamic behavior of jointed rock mass under blasting at high-stress conditions

Fang

et al. 2020

Shock and Vibration

Self Cite

Most of the roadway excavation is completed by the drilling and blasting method. With the increase of buried depth, the existence of ground stress will generate a significant impact on the rock blasting, especially on the smooth blasting. In this study, self-made homogeneous similar materials and digital image correlation methods were used to determine influence of ground stress on the smooth blasting under uniform explosive charge parameters and various in situ stress conditions. The results show that the crack outline after blasting changes from zigzag to straight in shape, and multifractal calculation results of the rupture section between blastholes show that the fracture surface becomes flatter as ground stress increases, which is conducive to roadway formation. The strain and equivalent strain rate obviously decrease as the distance between the blasthole and measuring points increases. The same trend occurs as the confining pressure goes up. Meanwhile, a postexplosion acoustic wave test indicates that confining pressure inhibits damage of the retained rock, which is consistent with strain and equivalent strain rate results. Finally, we discussed the crack propagation mechanism of rock in smooth blasting.

Section: Test Principle and Equipmentmentioning

confidence: 99%

In Situ Stress Effects on Smooth Blasting: Model Test and Analysis

Fang

et al. 2020

Shock and Vibration

Self Cite

“…Yang et al [22] used caustic experimental method to study the propagation laws of blast-induced cracks in pre-crack-containing media under the action of static compressive stress and analyzed the relationship between crack initiation angle and pre-crack angle. In addition, Yang et al [23] explored into the response of jointed rock mass to blasting under the action of static compressive stress field via model experiment, analyzed crack initiation mode and angle at joints and stress intensity factor and cracking velocity, and pointed out that static compressive stress field elevated the shear failure degree triggered by crack initiation at joints.…”

Section: State Of the Artmentioning

confidence: 99%

Experimental Study of the Dynamic Mechanical Behavior of Blast-Induced Cracks in Tensile Stress Field

Huang¹,

Ding²,

Xie³

et al. 2020

JESTR

Self Cite

The propagation behavior of blasting-induced cracks directly determines rock fragmentation and blasting effect. None of existing engineering blasting parameter design has considered the influence of initial tensile stress field on the propagation behavior of blast-induced cracks with a lack of theoretical and experimental guidance; therefore, the rock blasting effect in tensile stress field is far from ideal. The stress distribution and crack stress state around borehole under the coupling action of static tensile stress and blasting stress were determined based on the theory of elastic mechanics to reveal the propagation behavior of blast-induced cracks in the initial tensile stress field and the blasting fracture mechanism. Caustic method and digital laser dynamic caustic experimental system were combined to investigate and analyze laws influencing initial tensile stress and pre-crack angle on dynamic mechanical behavior, such as propagation velocity and dynamic stress intensity factor of blast-induced cracks in the tensile stress field. Results show that under the initial tensile stress field, the stress state of borehole wall in the direction of the vertical stress field is mainly circumferential tensile stress. Blast-induced cracks can easily experience crack initiation in this direction to form better crushing effect. The tensile stress field exhibits an inhibitory effect on the propagation of blast-induced cracks parallel to the direction of tensile stress while having a facilitating effect on the propagation of blast-induced cracks perpendicular to the direction of tensile stress. As the tensile stress field is enlarged, the propagation velocity, dynamic stress intensity factor, and propagation length of blast-induced cracks perpendicular to the direction of tensile stress can also increase. Furthermore, the enlarging pre-crack angle in the tensile stress field can postpone the attenuation of dynamic stress intensity factor and propagation velocity of blast-induced cracks and enlarge their attenuation amplitudes. This study can provide a theoretical guidance for engineering blasting practice in tensile stress field.

Advances in Civil Engineering

“…Guo et al have made a detailed study on the construction technology and mechanism of cumulative blasting and applied cumulative blasting to improve the permeability in high gas and low permeability coal seams [9][10][11]. A large number of literature show that radial decoupling coefficient seriously affects the blasting effect, but these results are mostly based on conventional blasting or slotted cartridge [12][13][14][15][16]. At present, scholars have seldom studied the effect of radial decoupling coefficient on the stress wave propagation and the crack propagation in cumulative blasting.…”

Section: Introductionmentioning

confidence: 99%

Study on the Decoupled Charge Effect in Deep‐Hole Cumulative Blasting of Coal Seam

Song

Guo

et al. 2019

Five models of cumulative blasting are established by using ANSYS/LS-DYNA to study the effect of decoupling coefficient on cumulative blasting to improve coal seam permeability. The formation and migration process of the shaped energy jets with two kinds of decoupling coefficient are compared and analyzed; also, the propagation of explosive stress waves is represented. The result showed that the air in the blast hole is the key to the formation and migration of the condensing jet. The air in the hole also could reduce the attenuation of stress wave in a certain range. However, if the decoupling coefficient is too large, the air in the hole will consume excessive explosive energy, which is also not conducive to energy transfer. Therefore, there is an optimum decoupling coefficient which can minimize the coal crushing area, increase the coal fissure area, and improve the gas extraction rate. Besides, the cumulative blasting tests were carried out in a coal seam. The test results show that decoupling charge could effectively improve coal seam permeability, and the blasting effect was better when the decoupling coefficient is between 1.67 and 2.