Research On The Degrading Effects Of Mechanical Properties Of Intermittent Jointed Sandstone Under "Water-Rock" Interaction

Since the impoucdndment of the Three Gorges Reservoir,a hydro-fluctuation belt of30 m has generated on the bank slope by the varied reservoir water level.Reservoir water level fluctuation makes partial rock mass of water alternate between saturation and air-dried state periodicity.This constant soaking-air drying water-rock interaction circulation(later refers to water-rock interaction)causes irreversible gradual damage on bank slope rock mass,which leads to the mechanical properties deterioration of rock mass and increasing development of joints and fractures inside,affecting the stability of slope.Based on the analysis above,typical sandstone in hydro-fluctuation belt of the Three Gorges Reservoir was selected as the research object,to make jointed sandstone samples with different dips of joint.The soaking-air drying cycle test was carried out to simulate the reality reservoir water level fluctuation process of hydro-fluctuation belt,for the analysis the mechanical properties of sandstone effected by joint dips and water-rock interaction.On the basis of physics and mechanical properties degradation law and deformation and failure mode of rock sample,the degradation mechanism of the jointed sandstone under the water-rock interaction was discussed in the paper.The main research results are as follows.1)Through the acoustical properties test of samples with different dips and depth of joint and complete ones,the samples were selected to weak test dispersion,and it is found that the ultrasonic wave has strong anisotropy in the propagation of jointed sandstone rock mass,which is influenced by the dips of joint and filler.Except for the sample of 90,wave velocity of rock samples increased with the dips of joints.2)Through the uniaxial and triaxial compress tests of the jointed sandstone samples,the whole stress-strain curves are obtained,and the strength,deformation characteristics and strength parameters law with joint dips are analyzed for anisotropy study of jointed sandstone.It can be found that sample mechanics characteristics curves with varied joint dips appears u-shaped,which obtains the minimum value near 60 °.Based on damage photos and crack development drawings of samples,the influence of joint dip and confining pressure on the failure mode of the sample are discussed in the paper.3)Through the uniaxial and triaxial compress test of the jointed sandstone samples on different water-rock interaction,the deterioration law of strength and deformation characteristics under water-rock interaction was analyzed.Under the water-rock interaction,the mechanical characteristics of the samples decreased gradually with smaller decreasing amplitude,and then tend to be stable.And the damage deterioration formula under water-rock interaction is set up,for the better response of the law above.The D-P yield function of jointed sandstone is proposed considering the deterioration effect of water-rock interaction.4)Through the density and wave velocity analysis of sandstone samples under different water-rock interaction,based on microscopic structure change process of sandstone sample,the water-rock interaction effect on failure mode of rock is analyzed,and the damage and deterioration mechanism of sandstone samples under water-rock action also discussed in the paper.