A serials of loading-unloading experiments of marble in Jinping II hydropower station, China, are carried out to investigate its failure mechanism under complex stress condition. It is found that, the marble failure process is divided into five stages, including initial crack closure, linear elastic stage, damage development, macro-crack development and rock structure stage. During the initial crack closure stage, different confining pressures produce different initial crack volumetric strain and different compressible extents of initial crack which indicates the dominant effect of confining pressure during the initial crack closure stage. The results obtained from confining pressure reduction test show that the inflection point of volumetric strain of Jinping II marble always lags behind the unloading point and the macro failure happens at 80%-95% of peak stress. This behavior plays an important role to control the support time when tunnels are excavated and provides a theoretical basis for preventing the failure of hard rock under loading-unloading condition.


With the development of human's society, the scarcity of energy becomes increasingly serious. Jinping II hydropower station in China [1,2], was built to solve part of the energy problem. With the excavation of tunnels, some complex mechanical behaviors, such as highly nonlinearity, discontinuity and anisotropy, of the deep-seated marbles were exhibited. Therefore, it's important to study the behavior of marble in Jinping II hydropower station which will help us to understand its complex failure mechanism.

In this paper, a serials of loading-unloading experiments of Jinping Marble were conducted. The volumetric strain, crack volumetric strain, equivalent plastic strain and the relation of stress-strain are combined to analyze its failure mechanism. Especially, the crack volumetric strain can reflect the damage development in the rock. This variable first introduced by CD. Martin[3-5] and then widely used to study on the deep-seated rock by many researchers[6-11]. However, the variable is rarely used to study on the mechanical behavior of rocks under loading-unloading conditions.

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