Factors affecting the durability of selected weak and clay-bearing rocks from Turkey, with particular emphasis on the influence of the number of drying and wetting cycles

Weathering can induce a rapid change of rock material from initial rock-lik e properties to soil-like properties. The resistance of a rock to short-ter m weathering is described through a durability parameter called the slake d urability index. As durability is an important engineering parameter, parti cularly for weak and clay-bearing rocks, it was assessed by a number of tes ts. The main purpose of this study is to assess the influence of the number of drying and wetting cycles and controls of mineralogical composition and strength on durability. For this purpose, 141 samples of different types o f weak and clay-bearing rocks were selected from different parts of Turkey, and relationships between the above-mentioned rock characteristics were st atistically investigated. The samples were subjected to multiple-cycle slak e durability testing, X-ray diffraction (XRD) analysis and uniaxial compres sion testing. Tn addition, to assess the influence of mineralogical composi tion on durability, the mineral contents of the original material and the m aterial passing from the drum of the slake durability apparatus after each cycle were also determined by XRD. The results indicate that the type and a mount of clay minerals are the main factors influencing the variations of t he slake durability index in all samples. The durability of the day-bearing rocks studied correlates best with the amount of expandable clay minerals. A strong relationship between the uniaxial compressive strength and the fo urth-cycle slake durability index is found only for the marls among the roc k types studied. Assessment of gradation results of the spoil pile material s consisting of day-bearing rocks also reveals that the increase in percent age of fines in old piles is indicative of material degradation, as is evid ent by multiple-cycle slaking. It is emphasized that two-cycle conventional slake durability testing did not appear to offer an acceptable indication of the durability of weak and clay-bearing rocks when compared with multipl e-cyclic wetting and drying. Comments on the performance of the test are ma de that aim to make the testing process and interpretation of the results m ore reliable. (C) 2000 Elsevier Science B.V. All rights reserved.