Prediction of rockburst in water conveyance tunnel: a case study of Gelas tunnel

Abstract

At the presence of undesirable geological conditions, including rock masses with high overburden, crushed zones and faults, folds, dikes and other abnormalities, rockburst has become a critical safety problem in Gelas tunnel, a water conveyance tunnel, wherein some sections overlying strata exceed 600 m. The main goal of this study is to determine the possibility of rockburst and its level along the second part of the Gelas tunnel. In order to study the mechanisms of rockburst occurrence in Gelas tunnel, measurements of in situ stress, geological investigation, uniaxial compression tests, and analytical approaches are carried. So, in this study, some analytical approaches, including Linear elastic index, Tangential stresses criterion, Brittleness coefficient of rocks, and method of stresses are used to predict rockburst in 17 sections of the tunnel path. The average result shows that all the selected sections in the tunnel path have the potential of occurring rockburst at a range of low to moderate. About 65 percent of the sections are exposed to moderate risk of rockburst occurrence; and the remaining 35 percent are exposed to low risk of rockburst occurrence. The comparison between applied methods shows a lack of consensus conformity among them. The brittleness coefficient of rocks method turned out to be as the most conservative approaches for predicting rockburst occurrence since by this approach most of the sections in the tunnel path are susceptible to high risk of rockburst occurrence. According to the average result, fault and Dolomitic zones with high overburden have the highest risk of rockburst occurrence.