ABSTRACT:

The durability of sixty-eight shale samples from the Appalachian region was evaluated using a combination of Jar Slake Tests, thin section and X-ray diffraction analyses, as well as fractal theory. Of the sixty-eight samples tested, fourteen degraded into mud, and fifty-four experienced little or no changes. Kaolinite was the main clay mineral in the shales. Shales composed of kaolinite slake as a result of pore-air compression. Pore-air compression is the result of water suction by the pores. Pore-air compression is favored by small pore radii. The samples that slaked had pore diameters equal to or smaller than 0.06 mm. However, many of the samples that did not slake also had pores with diameters smaller than 0.06 mm. Using fractal theory, this study presents an explanation for why the shales with small pore sizes did not slake. The explantion is based on the degree of roughness of the pore walls. It was determined experimentally and theoretically that pore wall roughness had a negative effect on the development of pore-air compression in the shales with pore

diameters smaller than 0.06 mm.

1 INTRODUCTION

Shale is the most common group of rock material found in the Earth's crust. Because of their abundance, shales have been used in the construction of earth embankments for highways as well as earth dams for the retention of water. Shales also form part of the roof system in underground coal mines and of natural or engineered slopes. Many types of shales slake when in contact with water. Thus, shale degradation has been associated with many infrastructure problems such as settlement and instability of highway embankments, subsidence in areas with coal mines, and slope instability (Olivier, 1979; Cununings et al., 1983). To date our knowledge of the mechanisms of shale slaking is incomplete (Pappas and Vallejo, 1997). The purpose of this study is to present a microstructural analysis to investigate how pore geometry in shales influence their degradation when in contact with water. The pore geometry will be evaluated using fractal theory (Mamndelbrot, 1977).

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