Ding-Ping Xu

A Comparative Study on the Shear Behavior of an Interlayer Material Based on Laboratory and In Situ Shear Tests

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 via in situ direct shear and laboratory shear tests. A comparative study was performed based on the two test results. It has been observed that both tests show elastic perfect-plastic behavior. A significant heterogeneity of the samples has been identified under both laboratory and field conditions. The samples’ disturbance seems to be a less important factor than the samples’ variability. The size effect has been evidenced by the friction angle obtained in the laboratory on small samples, which is greater 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 the initial degree of saturation has been identified. Comparisons between the results of the field tests and those from the laboratory tests show good consistency in terms of the effects of the clay fraction and the initial degree of saturation, indicating a relatively secondary effect of the sample size and variability.

An experimental study on the shear strength behaviour of an interlayered shear weakness zone

In order to evaluate the overall stability of the underground powerhouse at the proposed Baihetan hydropower station in China, the shear behaviour of a weak interlayered soil in the host rock and the soil/host rock interface was investigated in the laboratory by direct shear testing under different degrees of saturation. Shear creep tests were also undertaken on the interlayered soil. Typical results obtained from the multi-sample method (MSM) and single-sample method (SSM) are presented, which show that the shear behaviour of both the interlayered soil and the soil/rock interface is elastic perfect-plastic without dilatancy. It was not possible to determine the shear strength parameters using the multi-sample method due to the heterogeneity of the interlayered soil in terms of mineralogical composition and physical properties. Creep of the interlayered soil was found to be insignificant. The shear behaviour of the soil/rock interface depends strongly on the interface morphology: the rougher the interface the higher the shear strength.RésuméAfin d’évaluer la stabilité d’ensemble de la centrale souterraine de la future usine hydroélectrique de Baihetan en Chine, les comportements en cisaillement d’un matériau de type sol présent dans la roche hôte et celui de l’interface entre ce sol et la roche hôte ont été étudiés au laboratoire en réalisant des essais de cisaillement direct. Différents degrés de saturation ont été pris en compte. Afin d’évaluer le comportement au fluage du sol, des essais de fluage en cisaillement ont également été réalisées. Des résultats typiques obtenus à partir de la méthode multi-échantillons (MSM) et de la méthode basée sur un seul échantillon (SSM) sont présentés, montrant clairement que le comportement en cisaillement à la fois du sol et de l’interface sol/roche est élastique parfaitement plastique sans-dilatance. Il faut noter que, du fait de l’hétérogénéité du sol concernant sa composition minéralogique et ses propriétés physiques, il n’a pas été possible de déterminer ses paramètres de résistance au cisaillement en utilisant la méthode MSM. Il a été établi que le fluage du sol était insignifiant. Le comportement en cisaillement de l’interface sol/roche dépend fortement de la morphologie de l’interface: plus l’interface est rugueuse, plus la résistance au cisaillement est forte.