Abstract:
The slaking phenomenon of geo-materials derived from weak rocks such as mudstone or shale may cause the deformation of earth structures. Thus it should be properly considered in the process of design and construction. Previous researches indicated that slaking causes variation in particle size distribution and change in mechanical properties. However, mechanism of slaking phenomena and its mechanical consequence needs to be studied carefully. Therefore, investigation of slaking and deformation behavior through several laboratory tests was performed. In order to discuss the fundamental slaking phenomena, laboratory experiments such as ordinary acceleration slaking tests, X-Ray Fluorescence tests (XR-F) and Scanning Electron Microscopy (SEM) observation have been performed. Moreover, in order to observe the slaking phenomena and its effect on compression behavior, we modified one dimensional compression slaking test in which cyclic processes of wetting and drying is given. Kobe mudstone and Kakegawa mudstone were used to perform one-dimensional compression slaking test. The experimental results of one dimensional compression slaking tests showed that particle crushing phenomenon during the compressive stress contributes to increasing compressibility. The compressive slaking revealed that slaking under reaction stress cause the large compression even the mudstone specimens compacted to medium density. The study also suggested that it is possible to describe the slaking phenomenon in a similar way as the particle-crushing phenomenon using the scaler grading index that represents particle characteristics.
Introduction
Weak rocks such as mudstone or shale are highly susceptible to the weathered. Such materials have a tendency to slake and soften when immersed or contacted to the water and as a result their strength diminishes gradually with time. Due to this natural obstacle, mudstone material has been mostly disposed as waste material. However, meanwhile dealing with economic considerations and environmental concerns, several earth constructions projects propose to utilize the crushed mudstones or shales as geomaterials. Since large embankment made of these materials is considered, long term stability problem may possibly appear from the occurrence of slaking (Wakinshaw and Santi, 1996; Botts, 1998; Yoshida et.al, 2002; Santi, 2006). One of these embankments located on the Tomei expressway in Makinohara district in Japan failed during the Surugawan earthquake in 2009, with subsequent field investigation and analysis identifying the primary cause to be slaking of the mudstone (Yasuda et.al, 2012).
The slaking behavior of weak rocks has been studied experimentally (Vallejo et.al 1993; Santi, 1998; Yoshida and Hosokawa, 2004) through slake-durability tests and other similar tests, in which a number of wetting and drying cycles are applied to evaluate the weathering resistance of weak rocks as shales, mudstones and siltstones. This has demonstrated that slaking cycles significantly affect the degradation process and evolution of particle size distribution in such rocks (Sadisun et.al, 2005; Gautam and Shakoor, 2013). Several studies have discussed the effects of various mineralogical, chemical, physical, and mechanical properties on the weathering characteristics of weak rocks, which have shown that rock-forming minerals have a dominant effect on the chemical weathering of sedimentary rocks (Chigira and Oyama, 1999; Bhattarai et.al, 2006; Schaefer and Birchmeir, 2013).
