An analysis on the slaking and disintegration extent of weak rock mass of the water tunnels for hydropower project using modified slake durability test

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.

Kajian Ketahanan Batuan Clay Shale Formasi Jatiluhur di Sentul City Jawa Barat

The mechanical properties of Clay Shale are very unique. When it is dry, it shrinks and hardens, butwhen it absorbs water, it swells and to some extent loses its shear strength so that the drop-instrength can occur suddenly even with its own weight. Due to the nature of the swell-shrink that arestrongly influenced by climate and weather, clay shale durability may decrease over time when indirect contact with air and water. Research on clay shale was done in Sentul City, Bogor - West Java,Indonesia on Jatiluhur formation, using dynamic slaking (slake durability test) and slaking static test.Dynamic slacking test is done in three times i.e. after sampling, after 3 months and after 9 months.Slake durability test results from 3 different drilling points, shows that within 9 months, has not seenthe decreasing effect of durability. With a low Plasticity index, the durability research in Sentul City isin medium durability to medium-high durability classification.

Durability Assessment of Clay-Bearing Soft Rocks By Using New Decay Index

Clay-bearing rocks are known as most important problematic weak rocks. Due to the importance of disintegration of clay-bearing rocks in engineering projects, several simple test methods have been proposed to assess durability of these rocks. In this study, a comprehensive research program was conducted on twenty different clay-bearing rocks to assess their disintegration characteristics under laboratory conditions. In order to carry out the research, at the first step some physical and mechanical properties of the studied rocks were measured. After that, three durability test methods were employed. These tests include the standard slake durability test to obtain index durability (Id2 ), slake durability test with sieving the remained materials in drum to obtain disintegration ratio (DR) and new time series slake durability test to obtain decay index (DI). The results of this research indicated that for most of samples, using the standardized slake durability index test (Id2 ) may not be adequate to understand the disintegration characteristics of clay-bearing rocks and shows overestimated values. The new decay index (DI) has overcome the most limitations of the standard slake durability test and clearly will realize deterioration potential of clay bearing rocks. Finally, based on the results of decay index a new durability classification was proposed.