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Response to changes in humidity of shales in tunnels
Kreidler, Mason Csaba
Kreidler, Mason Csaba
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2014
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2014
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Abstract
Slaking of shales has been known to cause a variety of problems in tunnels and mines, and on some occasions has resulted in catastrophic roof collapses. Usually, severe slaking is caused by shale's exposure to cyclical submergence in water and subsequent drying, but it has also been shown to result from fluctuations in humidity. To this date, a number of methods have been developed to anticipate how shale might respond to changes in humidity, yet these have relied on complicated and time consuming testing methods. As a result, the methods are not commonly used in the tunneling industry. In this study, a series of tests were used in an attempt to develop a method that addresses these concerns, making testing for slake sensitivity more accessible. Apart from immediate slaking responses, these tests were also used to examine the long-term effect that humidity exposure has on shale. Evaluating these reactions required performing some time-consuming tests, such as placing shale samples in humidity chambers, similar to those outlined in previous research. After cycles of humidifying and drying, the samples were subjected to standardized point load and slake durability tests to quantify the affect humidity has on the strength and slake durability of shale. After three cycles of humidifying and drying, the results of this study suggest that exposure to humidity impacts strength more significantly than slake durability. However, both properties are variable within and between rock types, and are therefore difficult to predict. The most significant impact on rock strength was instantaneous moisture content of the rocks when subjected to point load tests. Rocks recently taken from humidity chambers were significantly weaker than air-dried rocks of the same kind. Slake durability test results showed little dependence on pre-test moisture content, though exposure to at least one drying-humidifying cycle did increase slaking in some cases. Overall, little correlation was found between slake durability and point load test results. Consequently, developing a standardized testing method relying on these two properties is difficult.
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