Water tunnels built for hydropower passing through weak and heterogeneous rock mass pose challenges associated to slaking and disintegration, as they are first exposed to dry condition during excavation and are then filled with water to produce hydropower energy. Over the period of operational life, these tunnels are drained periodically for inspections and repair leading to drainage and filling cycles. The weakening of rock mass caused by cycles of drying, saturation and drainage may lead to the propagation of instabilities in the tunnels. Therefore, it is important to study the slaking and disintegration behavior of the weak rock mass consisting of clay and clay-like minerals. This paper assesses the mineralogical composition of flysch and serpentinite from the headrace tunnel of Moglicë Hydropower Project in Albania. Further, to determine the slaking and disintegration behavior of these rocks, extensive testing using both the ISRM, Int J Rock Mech Min Sci Geomech Abstr 16 (2): 143-151, (1979) suggested test method and a modified variant of this test are performed. Finally, comprehensive assessments, discussions and comparisons are made. It is found that the modified slake durability test better suits for the tunnels built as water conveying systems such as hydropower tunnels.
Adequate rock support in weakness zones that may contain swelling minerals poses one of the main challenges of excavating tunnels in hard rock conditions. Deformations under such conditions are influenced by several factors, including the properties of the rock mass, rock stress and the possible swelling potential of the minerals. Thus, dimensioning rock support may be challenging. To increase the knowledge regarding the processes behind deformations in areas of swelling gouge material, an experimental triaxial laboratory test of such material was performed. The main objective was to investigate whether the material might exert pressure under typical in situ stress conditions, or whether other processes might be dominant. In addition, the possible elastic and strength properties of such material were investigated. The testing was performed on reconstituted cores with material from four different locations in eastern Norway. The material was dried and then pressed into cores using a compactor. The triaxial testing consisted of four successive phases: pre-stressing 1; water addition under constant strain; pre-stressing 2 and failure. The results indicate that factors other than swelling pressure are the main causes of tunnel deformation, as no build-up of swelling pressure was observed during the water addition phase. Initially, the E-modulus and strength properties of the samples were very low, which can cause large, immediate deformations in situ. In addition, creep and possibly a reduction in the Emodulus during water addition seemed to cause time-dependent deformation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.