Abstract
This paper aims at providing a sound theoretical solution to auxiliary central hole and the cutting parameters. For this purpose, the forming mechanism of V‐cut cavity for cutting blasting was performed based on the hypothetical rock breaking mechanism of V‐cut blasting. A theoretical solution for increasing the critical depth of the auxiliary center cuthole and the criteria for increasing the cuthole diameter of various types of cutholes when the rock attributes, explosive properties, and cuthole dip angle are constant are proposed. (1) If charging length le < 0.75H/sin θ, no auxiliary cuthole is needed. (2) If 0.75H/sin θ < le < 0.75H/sin θ + (2∼4) × 0.1, a central vertical auxiliary hole is needed. (3) If 0.75H/sin θ + (2∼4) × 0.1 < le < 0.75(H/sin θ + Hi/sin θi), a shallow inclined hole is needed. (4) If le > 0.75(H/sin θ + Hi/sin θi), both the central vertical cuthole and the shallow inclined cuthole are needed. Meanwhile, the theoretical solution was verified by numerical modelling with ANSYS/LS‐DYNA. Moreover, the field implementation of the V‐cut and the auxiliary hole effectively improved the blasting effect in both efficiency and economy.
Highlights
The theoretical solution was verified by numerical modelling with ANSYS/LS-DYNA
During the tunnel excavation of V-cut blasting, the minimum burden of V-cutholes and the rock clamping force are bound to increase with the depth of V-cuthole
According to the results of numerical simulation calculations, it can be known that the method of undercutting with a central hole is conducive to reducing the occurrence of the bulged phenomenon, thereby forming a larger V-cut blasting cavity volume
Summary
During the tunnel excavation of V-cut blasting, the minimum burden of V-cutholes and the rock clamping force are bound to increase with the depth of V-cuthole. Soroush et al [8] analyzed the effect and sensitivity of the hole diameter and tunnel face area on blasting results in different blast models, pointing out that V-cut needed more cutholes than parallel cut in similar conditions. Liu et al [15] performed field tests on the stress concentration effect of central hole and proved that the hole enhances rock fragmentation via the reflection of tensile waves and thereby boosts the cyclic advancement. E main findings of their research include the following: the peak effective stress at the cuthole bottom was 40% higher in the presence than the absence of a central hole, revealing the importance of the central hole in the formation of cavity bottom; the in situ tests show that the per cycle advancement increased by 31%∼65% due to the addition of central cutholes under the conventional blast loads.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
