Abstract:
Ground vibration is an undesired effect of blasting in mining. In some situations where geotechnical slope performance is of concern, blast design gains an increased relevance as a variable to consider in slope stability. Several methods are available to assess the vibration levels produced by blasting in a mine operation (surface and underground). The scaled distance approach is the most widely used methodology to control vibration, however it has several limitations including the need for a complete set of data to find the ground coefficients used in the governing equation. This paper proposes a new methodology using a case study to predict and control ground vibrations produced by mine blasts based on the concept of the traditional signature hole technique. In the new methodology, a Monte Carlo scheme is used to produce a histogram of the predicted peak particle velocity and acceleration in locations of interest of the slope, according to the geometry, the timing, and the sequence of the blast design. This methodology has been used in surface coal mines to protect important infrastructure (power structures, gas lines, etc.) and in metal mines to control vibration levels to minimize the impact of blasting on the performance of large open pit slopes.
Introduction
In the mining production cycle, blasting is the most economical and efficient method to fracture and move the ground (rock material). It is commonly accepted that blasting has less influence on slope stability than geology and ground water. However, in some situations of sensitive slope behavior or where needed to protect important infrastructure, blast design takes increased relevance as a variable to consider.
Due to the nature of blasting, it is inevitable to damage, to some degree, the rock mass behind the slope face in an open pit operation. Along with rock mass damage, ground vibrations are another undesirable consequence of blasting. However, there are practical procedures based on experience and trial and error that may be implemented to minimize both rock mass damage and potentially damaging ground vibrations. The use of presplit blastholes and control of the amount of explosive detonated per delay are typical techniques used to help mitigate such unwanted effects. Recently, through the use of electronic initiation systems for mine blasting, timing and initiation sequence have become additional variables which allow for improvements in blast performance that warrant further study. Several methodologies are currently available to assess the vibration levels generated by a production shot. The most commonly used approach by the mining industry to assess ground vibration levels is scaled distance. However, in this approach, timing between holes or explosives charges is not a variable that can be assessed by that method. Moreover, there is no clear guideline as to what exactly constitutes a delay. This paper presents the application of a novel approach to predict and control ground vibration levels using improved signature hole technique or waveform superposition. The novel approach is semi-empirical, accounting for the vibration characteristics of the ground through the measurement of the signature waveform, including a Monte Carlo scheme, rendering a stochastic approach more preferable than a deterministic one.
