A Comparative Study on the Shear Behaviour of an Interlayer Material Based on Laboratory and In-situ Shear Tests

Abstract : In order to evaluate the overall stability of the underground powerhouse at the future Baihetan hydropower station in China, the shear strength of a weak intercalation soil in the host rock has been investigated by carrying out in-situ direct shear and laboratory shear tests. A comparative study was performed based on the two testing results. It has been observed that both tests show elastic perfect-plastic behaviour. A significant heterogeneity of the samples has been identified under both laboratory and field conditions. The samples disturbance seems to be a factor less important compared to the samples variability. The size effect has been evidenced by the greater friction angle obtained in the laboratory on small samples than that obtained in the field on larger samples. The clay fraction has been found to be an important factor; its increase reduces the friction angle and increases the cohesion. Without considering some particular data due to the soil heterogeneity, a negligible effect of initial degree of saturation has been identified. Comparison between the results from the field tests with that from the laboratory tests in terms of effects of the clay fraction and initial degree of saturation shows a good consistency, indicating a relatively secondary effect of samples size and samples variability.