SLOPES STABILITY STUDIES EXCAVATED IN A ROCK MASSES. CASE OF AHMED EL-HADJ QUARRY (LAFARGE)

Abstract

The study of the effect of blasting on bench stability is indispensable for the overall mine�s safety, in this perspective, we conducted a study in the limestone quarry, which is characterized by a highly fractured rock mass. While the quarry presents a steep topographic profile, the extraction is carried out on a single operating edge. The blasting operations in the quarry offer an unsatisfying fragmentation (high percentage of oversized boulders), important overbreak, and deformation to the bench�s face; these irregularities are problematic, and their continuity may cause serious instability to the system benchquarry slope. The study concerns several benches located on different levels of the quarry and aims to evaluate the extent of the blast-induced effects beyond the intended fragmentation section and to assess the bench stability under the blast effects. Then, propose practical solutions to limit the unwanted effects, starting by determining a more suitable blast design that allows a higher bench stability, and assures, at the same time, a satisfying and accurate rock mass fragmentation. The work is divided into two parts: First, a comparative study between two fragmentation analysis methods; a prediction and analysis of the fragmentation using the Kuz-Ram model, to assess the efficiency of blasts by the quarry�s current blast design. Then, by variating, some settings in the blast design, which serves as input for the Kuz-Ram model, we obtain, after a series of simulations, different predictions for the fragmentation. Subsequently, the design that presents improvements compared to the currently used design, in both fragmentation quality and bench stability, is chosen for application. Afterward, a digital image processing of the fragmentation, using the WipFrag software, is carried out for, both, the design obtained by the Kuz-Ram study and the precedent blast design. This method of analysis, contrary to the Kuz-Ram model procedure that presents as results of a prediction of the fragmentation, offers an actual and practical estimation of the fragmentation process. This technique consists in taking many digital images of the muck pile after each blast. These images are, then, processed by the WipFrag software, which estimates the average size of the fragments. Afterward, a general mean value of the average size of the material is estimated for all the blasts. Lastly, we compare the results obtained by the digital image analysis to those predicted by the first method. In the second part of this paper, a numerical modeling approach is adopted, by employing the Finite Element Method (FEM) and through the �Phase2� software. At this point, we perform simulations, in the static and dynamic conditions, on a numerical model of the quarry�s profile, the goal is to observe the various problems that could possibly occur during the blast excavation process and the permanent deformations that the rock mass might be subject to. The simulations in the dynamic conditions are carried out using the new proposed blast design.