Assessing the durability of mudrocks using the modified jar slake index test

As exposure to weathering processes or other changes in moisture content can be the cause of troublesome breakdown of many mudrocks, it is essential to have reliable means of predicting this behaviour. Although the ISRM slake durability test is the standard test used to distinguish between durable and non-durable mudrocks, the test does not always identify problematic materials. The dynamic nature of the test and the use of an arbitrary 2 mm drum mesh size are particular short falls. The test is too aggressive to characterize properly the behaviour of low durability mudrocks and slaking of samples to a fragment size greater than 2 mm is not measured, This paper reviews the various tests that have been used for predicting slaking potential. Comparative durability testing of 49 selected UK mudrocks ranging in age from Cambrian slates to Carboniferous Coal Measures is described. An evaluation of the performance of these materials in the one- and three-cycle ISRM stake durability test confirms the greater value of the latter. The modified jar slake test was found to be a suitably simple and accurate means of determining the durability of these mudrocks. Comparisons with the results of natural slaking trials confirm that the modified jar slake test presents a more detailed evaluation of the slaking potential of samples. In practice it is anticipated that the described test procedure will be used to provide data that would augment sample evaluation based on the ISRM slake durability test.