Abstract
The instability of the M'HAOUDATT pit is a major problem often encountered on the wall composed of a network of fractures located in unfavorable conditions for a very soft geological formation. Therefore, the trend in large open-pit mines is to use high-energy blasting to increase conveying performance and crusher throughput. The increase in blasting energy concentration can threaten the integrity of the pit wall. In this paper, we aim to find a suitable plan to stabilize the pit deposit, through analyses of structural and lithological data on the pit walls, with an interpretation of the lateral and depth extensions according to the geological complexity of the deposit. Followed by an analytical treatment of the current pit parameters. Data processing included core classification, kinematic assessment of failure mechanisms based on visual observations on the exposed faces of the expected pit. The results of the laboratory tests were also used to define the rock mass parameters used to establish a stable slope design. The analyses showed the need for an effective strategy to ensure that the slopes won’t be damaged by blasting. This wall control strategy aims to produce a fragmented bulk ore pile and a slope as designed and in good condition. A good understanding of the failure mechanisms is necessary to ensure better monitoring of the rock slopes of the M'HAOUDATT pit.
Highlights
Fracture survey processing shows a series of fractures of several families, which have the same geometric characteristics both at surface and at depth; The preponderance between all the families of discontinuities and the geological contact zones always generates the first phenomenon of instability in the M'HAOUDATT pit
During a visit to the M'HAOUDATT pit construction site, we found that the positioning of the blasting holes, their loading with explosives, and the undercutting of the loading shovels play a major role in the instability of the pit
We find that the Emulsion and ANFO explosives have a higher detonation velocity or density than is required to fragment the M'HAOUDATT pit rocks, and the ANFO explosive has a lower detonation velocity or density than is required to fragment the hematite ore [14]
Summary
The M'HAOUDATT mine is composed of several weak zones, generating instability all along the pit wall plus the roof and pit closures. The MHDT pit slopes have a specific design based on the nature of the terrain, the geomechanical parameters and the characteristics of the rock that constitutes it These parameters are used in empirical classification (RQD, Barton Q, Bieniawski RMR, GSI) to assess the quality of the terrain, and to take advantage of the correlation rules between the different methods to deduce the other parameters [7, 10]. These data allowed the analysis of the failure mechanisms that can realistically affect the slopes. A blast effect analysis was carried out to determine the response of the rock mass to the type of explosive used
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