engleski

Impact of weathering on slope stability in soft rock mass

The weathering of soft rock has been studied in various fields including geology, engineering geology, mineralogy, soil mechanics, rock mechanics and geomorphology. However, the relationship between influence of weathering and slope instability (i.e. landslides, rockfalls, surface erosion) is still not well understood. Surface degradation processes and local landslides occur quite frequently on slopes excavated in soft rock. As a result of these processes, safety of facilities at the bottom of these slopes is jeopardized and the cost of maintenance is usually considerably increased. At the same time the stability of facilities located at the top of such slopes is also submitted to increased risk. The excavation work in these materials (mostly clayey rocks such as marl, siltstone, mudstone, shale, claystone, etc.) can be performed only with use of heavy machinery (rock breaker) or explosives, as well as in any other rocks. However, in relatively short time after excavation, within couple of months, in which period excavated slope in marl is exposed to influence of atmospheric agents, the rock deterioration process starts both on the slope surface and within the interior of the rock mass. These processes can be observed on many natural slopes and on cuts excavated in flysch formations in the region of Dalmatia (Croatia). These formations are formed in the Eocene epoch and usually consist of marl as a main soft rock component. Information about marl strength at all phases of slope exploitation is of utmost importance for any stability analysis of cuts and slopes in this material. To provide data about the strength deterioration there should be a possibility to test degraded materials. Weathering processes fragment marl samples into smaller pieces thus the fragmented sample is very difficult to be operated with and be installed into a testing device. For the solution of this problem additions to the standard test procedure were used (Miščević and Vlastelica, 2009). Additions refer to the standard procedure of a direct shear test method (ISRM Suggested methods for determining shear strength in 1974) in order to enable testing of deteriorated samples. Results of this procedure are presented and discussed. The main scope of the presented study is to: identify the main influences on slope stability in marl rock formation, present some basic engineering observations or previous experiences on known examples of observed slopes in this material and propose solutions how to include those observations in future projects and studies. Also, it is important to emphasise the necessity of proper engineering solutions that prevent the development of the weathering process, which lower the potential of slope instability and the maintenance cost.

marl; slope stability; durability; weathering

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