Dynamic Properties of Weak Intercalation Encountered in Xiaolangdi Project on Yellow River

摘要

The deformation and strength of rock mass are dominated to a considerable extent by its soft and weak intercalations. The dynamic properties of the weak intercalations in the left hill mass of the Xiaolangdi Damsite, which is located in the downstream of the Yellow River, China, and which is mainly composed of sandstone with clay intercalations of Traissic time, have been studied through laboratory shearing experiments. The samples used in the experiments are from the site and contain gouge, clastic sediments, and materials with slickenside. Furthermore, the dynamic shear modulus and damping ratio are studied by a resonant column method using moulded samples. The experimental results under multi-cyclic loading on the model with soft and weak intercalations show that a non-linear relationship emerges between dynamic shear stress and strain, and that the strain is of obvious hysteresis. In case of increasing the total stress level, the dynamic strain will become bigger and bigger with the increase of the number of cyclic loading, and finally appears as plastic deformation. The experiments also show that the dynamic strength is closely related to the duration of dynamic loading or the number of cycles. The realtionship between the dynamic shear strength and the initial normal stress follows the Mohr-Coulomb Law. The dynamic friction coefficients are larger than the static ones. Another important fact is that the exsistence of smooth slickenside can reduce 50% of the cohesion and 30% of the dynamic friction coefficient. The method and results in this paper can reasonably be used to evaluate the dynamic stability of the left hill mass of the Xiaolangdi Damsite.