A Study on Change in Microstructures and Mechanical Properties of Clayey Soils Subjected to High Temperature Histories

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A triaxial test apparatus which can conduct consolidation, shear and permeability tests under high temperature conditions from 50℃ to 2OO℃ was developed in this study. In order to clarify consolidation and shear characteristics of clayey soils a series of consolidated-undrained triaxial compression tests was carried out using the developed triaxial test apparatus for kaolin clay and bentonite clay under several temperature conditions. As the results, it was found that mechanical properties of clay under 1OO℃ are on the extended lines forecasted from temperature effects below 1OO℃ and no significant change in mechanical properties of clay appears under about 1OO℃. It was also found that the compression strength increases for both kaolin and bentonite clays with the increase of test temperature, and the gradient of the critical state line decreases for kaolin clay but increases for bentonite clay with the increase of test temperature. Moreover, it was found that although the compression strength increases for both clays with the increase of test temperature, the increment of the compression strength corresponding to the decrease of the void ratio due to the increase of test temperature does not appear for both clays.A computer image processing method was developed in order to evaluate quantitative microstructures of clays. Density distributions of Scanning Electron Microscope photographs were measured and their power spectrum were analyzed in this method. It was found from the results obtained by this evaluation method that high temperature reconsolidated clays have a random structure and room temperature reconsolidated clays have an oriented structure.