Safety Factor of the Open-pit Bench from Rosia Poieni Quarry, Romania

In addition to the in situ and laboratory studies of the mechanical characteristics, it is necessary to carry out a calculation of the stability of the exploitation benches based on which it is possible to determine the breaking curve along which there is the greatest risk of sliding, and on the other hand the corresponding value of the safety factor. The level of +805 m was determined as the daily operational limit for the Rosia Poieni open-pit mine; benches were created based on this level by cutting horizontal slices with a thickness of 15 m, which is equivalent to the bench's height. Therefore, there were 23 benches in the Ruginis area and 27 in the Curmatura area. The general slope angle was set at 35°,the angle for which the tailings volumes and implicitly the opening-up coefficient were calculated. The stability analysis was performed for individual bench, 2 benches system and the general slope of the quarry (consisting of 24 benches), using two methods (Fellenius and Janbu). The obtained values are above 1.3 for individual slopes and two-bench system, respectively 3.754 for the general slope, and correspond to the imposed values by standards. A polygonal sliding surface was also modelled; these potential landslide surfaces may arise in the Rosia Poieni quarry's slopes due to the massif's natural cracking systems as well as secondary cracking caused by the operations employed for drilling and blasting (exploitation technology). The stability assessment was carried out using Hoek's graphical-analytical method, and the safety factor values found meet the requirement of being more than 1.3. In these circumstances, no further measures are required to increase the stability reserve.