Abstract:

Slates show typical anisotropic properties and it would change to clay after long term interaction with water, so some experiments were performed to study mechanical properties in different conditions. Microstructures of the minerals forming the rocks and the strength of the rocks in different absorption were measured. Single discontinuity theory was used to analyze the change of rock mass strength with the discontinuity inclinations, and the relationship between them was set up to explain the compression results. Then after analyzed the change of microstructures, water-weakening mechanism was studied. Some conclusions were drawn from the analysis:

  1. The deformation forms transferred with the different discontinuity inclinations, and it can be slided from discontinuities, sheared and the complex of the two forms and the deformation form changed from slide to shear when the confining pressure increased.

  2. failure strength of slates changed in a paradola line with the discontinuity inclination variation and the least angle is 51.7°;

  3. triaxial compression results showed that the slates weakened and the peak strength of the slates declined with the absorption increased in minus logarithm law; the elastic modulus decreased either;

  4. the grains of the slates bulged and the structure relaxed, which made the porosity increased without confinement and the volume bulge lagged behind the water absorption; As a result, slate rocks are easier to failure following the layer surfaces. Capillary effects and Rhehinder effects played a primary role in slate-water interactions through the results of microstructure and contact angle.

Introduction

Slates were formed from shale by light metamorphosing and textures, joints, layering and cracks prevailed inside which made the slates show typical anisotropic properties. For the purpose of evaluating the stability of open ditches and underground tunnels constructed in slates in some areas, it's necessary to systematically analyze the characters of slates. Furthermore, it was found that slates may change to clay after long term submerging in underground water in special conditions. Therefore, it was also needed to study the water-weakening properties of slates in different water contents. Recently, many researches were focused mainly on the anisotropic properties of slates in different ways. M. Brooks Clark et al. explained the anisotropic mechanical properties from the micro arrangement of mineral grains. Catalina M. Ltineburg et al. studied the range and distribution characters of pyrite in slate. The orientation of minerals made the magnetic field showed anisotropic and the strains under press had the same features. X ray diffraction analysis, SEM and TEM technology were used by Nei-Che Ho to analyze the array of mica and chlorite in slates from strata of Michigan. T.Heggheim et al. analyzed the change of mechanical characters and microstructures of chalk saturated with different seawater, glycol and brines and he brought a theoretical model to explain the mechanism. S.W.J. Den Brok et al. performed the experiments on natural quartzite at high temperature, different confining pressures and strain rates in the presence of added water to study the microcracks and new minerals.

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