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

Abstract

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.

Numerical Simulation of Rock Mass Structure Effect on Tunnel Smooth Blasting Quality: A Case Study

“…The research showed that the circumferential hole with a slotted tube charging structure significantly improved the overbreak phenomenon in the fault stratum. Yang et al [17] adopted self-made uniform similarity materials and digital image correlation methods and found that with the increase in buried depth, the ground stress exhibited a significant effect on smooth blasting, and the fracture surface tended to be flat with the increase in in situ stress. Qi et al [18] used the finite element numerical simulation software ANSYS/LS-DYNA to simulate the blasting process of the coupled charge in the peripheral holes in smooth blasting.…”

Fracture behavior in blasting under different static stresses and high stress unloading

“…These results are consistent with the conclusions of the previous literatures. 13,14 However, compared with the main crack length in specimen H4, the main crack length in specimen H12 is increased by 24.1 mm, meaning that the static stress can promote crack propagation again when the static stress exceeds a certain value. This phenomenon is different from the previous findings.…”

“…11,12 The model tests of smooth blast and presplitting blast under uniaxial loading were carried out, with results indicating that static stress has an essential effect on smooth blasting and presplitting blasting. [9][10][11][12][13] In addition, the single hole blast experiments and slit charge blast experiments were conducted under static stress using the caustic method. The results show that compressive stress increases the fractal dimension and promotes crack propagation when the compressive stress is parallel to the main crack.…”

“…However, the crack propagation is restrained when the compressive stress is perpendicular to the main crack. 13,14 The numerical technique has been frequently applied as a research tool to study stress evolution or fracture behavior in solid materials. For example, a numerical simulation based on Riedel-Hiermaier-Thoma (RHT) model was applied to investigate the influence of static stress on dynamic damage, 15 crack propagation, 16,17 pressure peak value, 18 crushed zone, 19 and fragmentation.…”

Experimental Study on Shock Wave Propagation of the Explosion in a Pipe with Holes by High-Speed Schlieren Method

“…However, photoelasticity and caustics methods meet difficulties in measurements near the borehole because data acquisition of isochromatic fringes in photoelasticity and shadow patterns in caustics method is very difficult in such an extreme condition. Digital image correlation (DIC) becomes a very effective method to study blast-induced stress waves [19,20], but this method needs speckles or reference points on specimen surface and does not work well for blast gases. Schlieren method can visualize propagation of shock waves and blast-induced products near the borehole because this method is sensitive to gas dynamics in transparent media.…”