Abstract

Bench blasting is the most common method of rock excavation in productive quarries. Properties of the rock mass and the discontinuities are factors that influence rock fragmentation but cannot be controlled. In this study, the remote sensing techniques known as Terrestrial Laser Scanning (TLS) and Close Range Photogrammetry (CRP) using Unmanned Aerial Vehicles (UAV) have been utilised to generate 3-dimensional (3D) models of rock surfaces using Topcon ScanMaster and Agisoft Photoscan software. From the data obtained, rock mass can be classified using rock mass rating (RMR) and geological strength index (GSI); the blastability index (BI) is then obtained for blast design. A 3D model of the blasted rock surface is established based on pre and post-point cloud data. It can be concluded that the TLS and CRP methods, using UAV, can be used as complementary methods when classifying the rock mass and establishing the 3D finite element model of a quarry face.

1.
Introduction

The aim of blasting is to extract the largest possible quantity of rock at minimum cost in the safest manner possible whilst minimising side effects like flyrock, noise and ground vibration. Mackenzie (1966) mentioned that blasting is the cheapest way to fragment rock. Rock fragmentation has been the subject of much research because of its direct effects on the costs of drilling and blasting as well as the efficiency of the subsystems, such as loading, hauling and crushing in mining operations (Goodman &; Shi, 1985; Dershowitz, 1993; Faramarzi et al., 2013). In order to get good fragmentation during blasting, geometrical information such as discontinuities in the rock mass, needs to be clearly identified as this can help when designing the blasting pattern etc. Adhikari &; Gupta (1989) mentioned that rock mass properties are important parameters in a blast design and understanding the influence of geological discontinuities and the physico-mechanical properties of the rock is fundamental.

Characterisation of the rock mass requires the gathering of information through geological fieldwork, conventionally being collected manually using a compass-clinometer and a tape measure. The conventional methods are simple and effective, however the collection of data via fieldwork can be a hazardous, time consuming process and data quality may be affected by the user's level of experience (Slob et al., 2010). Tannant (2015) highlights some of the drawbacks of hazard assessment of rock faces, such as:

  • safe access to the rock face to carry out geological mapping often does not exist,

  • it is difficult to measure the orientation and geometry of large geological structures such as faults by simply measuring an orientation where a scanline crosses the fault, and

  • mapping with a compass at the base of a steep slope exposes people to the risk of harm from rock falls.

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