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

2019 ◽  
Vol 79 (4) ◽  
pp. 1919-1937 ◽  
Author(s):  
Lena Selen ◽  
Krishna Kanta Panthi ◽  
Gunnar Vistnes
Keyword(s):  
Rock Mass ◽  
Test Method ◽  
Weak Rock ◽  
Hydropower Project ◽  
Durability Test ◽  
Slake Durability ◽  
Operational Life ◽  
Heterogeneous Rock ◽  
Weak Rock Mass ◽  
Slake Durability Test

AbstractWater 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.

Seismic repeaters linked to weak rock-mass creep in deep excavation mining

2020 ◽  
Vol 222 (1) ◽  
pp. 110-131 ◽  
Author(s):  
J L Kinscher ◽  
F De Santis ◽  
N Poiata ◽  
P Bernard ◽  
K H Palgunadi ◽  
...  
Keyword(s):  
Rock Mass ◽  
Template Matching ◽  
Double Difference ◽  
Propagation Mechanism ◽  
Weak Rock ◽  
Exact Nature ◽  
Seismic Triggering ◽  
Heterogeneous Rock ◽  
Depth Analysis ◽  
Weak Rock Mass

SUMMARY Seismic repeaters are a phenomenon rarely observed in mining environments. In this study, we show that repeaters and associated aseismic slip can be the governing mechanism behind seismic triggering in response to excavation mining, providing new perspectives for rethinking and improving standard procedures for seismic rock burst hazard assessment and mining monitoring. Evidence comes from an extensive multiplet analysis on dense spatiotemporal microseismic event clusters (−2.5 < Mw < 1) that was recorded by a local microseismic network at the Lappberget orebody in the Garpenberg mine in Sweden at around 1 km depth. Analysis involved template matching, clustering, double-difference relocation, source parameter and mechanism estimation, as well as interevent time analysis. The results show that almost 80 per cent of the analysed events can be interpreted as seismic repeaters. Source mechanisms demonstrate systematic strike-slip faulting with a significant reverse faulting component, indicating that triggering of the repeaters is sensitive to increases in the horizontal compressive stresses. We suggest that seismic repeaters represent brittle frictional parts (asperity) of creeping, planar shaped, pre-exiting structures of several metres composed of weak rock-mass materials (e.g. talc) associated with strengthening friction behaviours. This repeater model and the here used definition of asperity thus slightly differs from its meaning in classical seismological models where repeating events are related to the locked fault patches along a creeping fault. In addition, we identified different asperity types for the different repeater families that we interpret as different friction properties. Some multiplet families represent rather a transitional case between multiplet and repeater occurrences that might imply a mixture of weakening and strengthening friction processes, that is, creep and brittle rupture along neighboured plane shaped anisotropies in a heterogeneous rock mass. The exact nature of asperities and seismic and aseismic coupling of the rock mass as well as the propagation mechanism of strain and stress associated with short-term (days to weeks) and long-term (months to years) post-blast creep remains uncertain and needs to be addressed by future investigations. The understanding of these processes is particularly important for assessing hazard of larger dynamic ruptures.

Controls on shale durability: the response of two Ordovician shales in the slake durability test

1982 ◽  
Vol 19 (1) ◽  
pp. 1-13 ◽  
Author(s):  
D. J. Russell
Keyword(s):  
Durability Test ◽  
Georgian Bay ◽  
Slake Durability ◽  
High Durability ◽  
Calcite Cementation ◽  
Slake Durability Test

The slake durability test has been proposed as a means of predicting the engineering performance of shales. Testing of sections in the two major shale units of Ontario show that the test is capable of making distinctions between apparently similar shale samples. Queenston Shale has generally lower durability than the Georgian Bay Formation samples. Inspection of the shale fabric shows that this is due partly to inefficient cementing by calcite in Queenston Shale, but is primarily because the microcracks in Queenston Shale are more curved than those in Georgian Bay Formation. Variation in shale durability within the shales is controlled by mineralogy. In Queenston Shale, it is controlled almost entirely by calcite cementation. In Georgian Bay, where hard bands (shaly limestone) are present, these dominate the test, giving a high durability. However, pure shale durability is controlled by clay content.Comments on the performance of the test are made that aim to make the testing process and interpretation of the results more reliable. The method appears suitable for shale index testing and should be used as widely as possible in order to establish reliable correlations.

Sign in / Sign up

Export Citation Format

Share Document