Relative Durability of Shale -- A Suggested Rating System

The inability to predict the degradation tendencies of shale has resulted in numerous failures of projects where shale was used as a construction material. Because shale does not fit neatly into either a soil category or a rock category, the tests that are commonly used to classify soil or rock are in many instances not totally suitable for classifying shale as to its long-term behavior properties. Thus, special classification tests of shale types has become necessary. The durability or shale relates to how well it can withstand its changing environment and still retain its initial properties. Strength, expansion characteristics, and permeability play a part in the durability of a shale. A good classification system would incorporate in some manner these parameters to reflect the short-term and long-term durability of the shale. A new method of predicting shale durability has been developed based upon an analysis of a battery of index tests. Using multiple regression techniques, six tests have been shown to reflect the overall durability of shale. One of these tests is a new modification of the slake durability index test. These tests have been incorporated into a simple linear equation which can be used to obtain a durability rating on a scale of 0 to 100 for a particular shale