Study on Delay Time and Rock Mass Damage Patterns in Pre-Split Blasting of Water-Saturated Skarn in Alpine Regions

In order to solve the problem of ineffective pre-splitting blasting and reduce the damage caused to preserved rock bodies in the Niukutou open-pit quarry in the alpine region of Qinghai Province, China, this study investigated the influence of different delay times on the damage caused to the rock mass, combining numerical calculations with field tests. Using the finite element software ANSYS/LS-DYNA 19.0 and based on the constitutive model of saturated skarn, numerical models of pre-splitting blasting with four different delay times (0 ms, 12 ms, 18 ms, and 24 ms) were established. These models systematically analyze the damage evolution of rock and the effective stress distribution in specific elements under different delay times. The results indicate that a maximum damage depth of 32.56 cm occurs when the inter-hole delay is 0 ms, while a minimum damage depth of 30.61 cm is observed when the inter-hole delay is 18 ms. Further analysis reveals that the peak effective stress is highest when the inter-hole delay is 0 ms, and that the peak effective stress at 18 ms is higher than that at 12 ms and 24 ms. Considering the need to control the damage caused to the surrounding rock and the blasting effectiveness, the best pre-splitting blasting effect is achieved with an inter-hole delay of 18 ms. Field tests show that the damage depth of the retained rock mass is 1.62 m when the inter-hole delay is 0 ms; however, it decreases to 0.90 m when the delay is 18 ms, representing a 44% reduction in rock mass damage depth. This study provides theoretical support and practical guidance for the optimization of pre-splitting blasting in saturated skarn in alpine regions.