Assessment of physical disintegration characteristics of clay-bearing rocks: Disintegration index test and a new durability classification chart

Clay-bearing rocks cover large areas on the earth surface and are highly sensitive to changes in their water content. It is well known that strength and deformability, properties of these rocks also deteriorate due to wetting and drying processes, causing numerous engineering problems. Due to the importance of disintegration of the clay-bearing rocks in geo-engineering practice, several simple test methods and classification systems have been proposed to assess durability The slake durability index test is one of the most widely used of these tests. However, due to mechanical breaks occurring during the test, immersion of samples in water for only 10 min and the assumption that fragments larger than 2 mm are durable, the slake durability test has some limitations. In addition, the field behaviour of clay-bearing rocks and the associated disintegration have not been fully considered in previous studies. In this study, a comprehensive research program was conducted on different clay-bearing rocks selected from Turkey to assess their disintegration characteristics under both field and laboratory conditions. Based on field and laboratory investigations, new approaches and a durability classification system are recommended to assess disintegration characteristics of clay-bearing rocks. The disintegration index test suggested in this study can minimize some of the limitations of the slake durability test. The comparison between the disintegration index values of the laboratory specimens and those of the samples from the same outcrops exposed to atmospheric conditions for 1 year showed close agreement. Based on these observations, a durability classification system consisting of six classes is suggested. The proposed classification system uses a new parameter called slake durability rating to determine the degree of disintegration of any clay-bearing rock. In addition, general information related to physical and mechanical properties of any class can be obtained from the explanation part of each class. This system may be useful to practitioners for identifying the type and degree of disintegration that may occur on a freshly exposed rock face. (C) 2009 Elsevier B.V. All rights reserved.