The Creep Mechanism Of Red-layer Soft Rock Under Water- Rock Interaction At Three Gorges Reservoir Area

Weak rock with lower strength would behave as remarkable rheological characteristics under the effect of long-term external loads. Slope stability problem of reservoirs caused by water-rock interaction would be a realistic problem which is severe and inescapable as a host of hydropower engineering projects are under construction and a build-up of reservoirs are developed, thus it’s meaningful to conduct further study of the characteristics of the weak rock in the hydro-fluctuation belt. This paper aims at uncovering the mechanical properties of red-bed soft rock through laboratory test. The main research contents are as follows:1)Conduct uniaxial compression test, triaxial compression test and split tensile test for red-bed soft rock under different soaking-air drying circulation periods with RMT-150 C rock mechanics testing system to study its strength, deformation and destruction characteristics under different water-rock interaction periods.2)Apply grade loading creep test for red-bed soft rock under 5Mpa surrounding pressure by triaxial creep testing machine controlled by RLW-2000 microcomputer, and analyze the characteristics of creep deformation and rate deterioration under different water-rock interaction periods for each loading grade, especially the sample under failure stress; identify the long-term strength of the sample by the method of isochronal curves, and introduce the notion of failure strength ratio and long-term strength ratio to comparatively analyze the proportion relationship between the peak value of triaxial loading and failure stress of grade creep, as well as long-term strength and failure stress of grade creep; analyze the destruction characteristics of the sample under different water-rock interaction periods.3)Adopt SEM electron microscope to scan the photos, thus analyze the characteristics and principles of the dynamic change of the red-bed soft rock under different water-rock interaction periods, and take a research of the micro-characteristics deterioration mechanism according to the micro-structure, secondary porosity, longitudinal wave velocity, density and solution ion concentration of the sample; analyze the macro-characteristics deterioration mechanism on the basis of the sample’s deformation, strength and failure characteristics, and study the failure mechanism of the red-bed soft rock sample under different water-rock interaction periods by analyzing the deterioration mechanism under different micro-characteristics, macro-characteristics and soaking-air drying circulation4)Take visco-elastoplastic model to simulate the creep properties of the red-bed soft rock under lower strength on the basis of the full curve of grade loading creep test. Make up a new non-lineal damage creep model by introducing damage variable to conduct non-linear improvement for the viscosity coefficient of the viscous component under accelerating creep stage and taking stress and time as triggers under the consideration of the mechanic damage characteristics at this stage on the basis of visco-elastoplastic combination components with high stress level. Apply optical identification for the parameters in the non-lineal damage creep model with Levenberg-Marquardt non-linear optimized least square method, and conduct rationality analysis to the model.5)Create a creep constitutive model of red-bed soft rock, which takes the effects of water-rock interaction damage and mechanic damage into consideration, on the basis of the non-linear damage creep model regarding to red-bed soft rock under different water-rock interaction periods, and conduct fitting for the creep curves of different samples of the model. The model would be favorable to describe the non-linear creep characteristics of the red-bed soft rock under the effect of water-rock interaction if it would present high relevancy.