Experimental Study on Notched Directional Blasting in Tensile Stress Field

Abstract

Notched blasting has been extensively applied as a traditional directional blasting method. At present, the measurement of notched blasting effect and rock fragmentation is mainly decided by the propagation behavior of blast-induced cracks. However, the influence of initial tensile stress field on such behavior is rarely considered in existing engineering blasting process, resulting in the non-remarkable directional fracture effect of tensile rock mass. To reveal the propagation behavior of the propagation behavior of blast-induced cracks in the initial tensile stress field, as well as the fracture failure mechanism, the stress distribution state and propagation mechanism of the blast-induced cracks near the notched hole under the combined action of initial tensile stress and blasting stress were determined on the basis of the theory of elastic and fracture mechanics. The combined dynamic-static loading device and digital laser caustic experimental system were used to conduct the planar model failure experiment under the joint action of the initial tensile and blasting stress. The influence laws of the initial tensile stress and notch angle on the propagation length and velocity of the blastinduced main cracks, as well as the stress intensity factor at the crack tip, were also investigated through the experiment. The results showed that, (1) In the initial tensile stress field, as circumferential tensile stress was generated at the blasthole wall by initial tensile stress, the blast-induced main crack could be more easily propagate in the direction perpendicular to the initial tensile stress. (2) When the angle between the notch and the initial tensile stress was 45°, the initial tensile stress enlarged the propagation length of the main crack, and the propagation mode transitioned from Mode I to I-II mixed mode. In the meantime, the main crack deflected perpendicular to the initial tensile stress. (3) When the notch was parallel to the initial tensile stress, the main crack demonstrated a linear propagation along the direction of initial tensile stress. The initial tensile stress promoted the generation of the secondary cracks in the two sides of the blasthole and shortened the propagation length of the main crack, thereby reducing the stress intensity factor of the main crack. Results can serve as a reference for directional blasting in the initial static tensile stress field.

Study on Rock Damage Mechanism for Lateral Blasting under High In Situ Stresses

“…Hu and Lu [8,9] studied the formation and propagation of crack induced by presplitting blasting in highly stressed rock mass via a mathematical model and concluded that the in situ stress can restrain the development of cracks between the presplitting holes when the in situ stress is perpendicular to the crack face. Yang and He [10,11] experimentally investigated the influence of confining pressure and ratios of horizontal-to-vertical pressure on the blast-induced rock fracture. The results showed that the direction of crack growth was largely controlled by the hoop tensile stress and biaxial pre-pressure ratio.…”