| Water-rock interaction exists widely in nature, which is the most active and important factor for a variety of geological disasters. The three gorges project will be completed; and the reservoir water will be raised to 175m and reduced to 145m every year. During the fluctuation of the reservoir water level, the quality of rock mass of the bank slopes would be deteriorated in water-rock interaction of "saturation-air dry" cycles, and it would further cause great damage to stability of the bank slope. So it is necessary to study water-rock interaction mechanisms and effects at the fluctuation of reservoir water level systemically, and determine the physical parameters of rock and soil mass, which can be applied in slope stability analysis and it would reveal the impact of the water-rock interaction on the slope stability.Based on theoretical analysis,a detailed study have been launched and experiment is considered as a main research methods:(1)The ultrasonic-rebound comprehensive method was applied to the rock sample selection which has the advantages of two methods. In order to get the accurate results, the rock specimens which may cause discrete results can be selected out first before the laboratory test. Practice shows that such a comprehensive sampling method has good applicability. At the same time, the ultrasonic-rebound method is quit useful to predict the compressive strength.(2) The inherent differences in the sample determine the differences of initial strength. Here try to propose a strength correction method, a strength prediction equation considering rebound value and strength of rock. It is equivalent to revise the initial strength of each specimen to the same standard, and then the law can be better reflected by the experiment results in a comparative analysis.(3) Water-rock interaction includes three aspects:physical, chemical and mechanical effects, the destruction of bank slopes would be the comprehensive result of those three aspects effects. Due to the proportion of different effects changes at different periods of water-rock interaction, failure mechanism of rock slope is not the same as well. So, the impact of water-rock interaction mechanism on bank slope during fluctuation of reservoir water level should be considered to divide in three phases:the decrease, the rise and stationary of reservoir level. Meanwhile the effects of "saturation-air drying" should be mainly concentrated. The water-rock interaction mechanisms is summarized as five aspects:mechanical weakening mechanism, local stress concentration mechanism, physical weakening mechanism, chemical weakening mechanism, cumulative damage mechanism of "saturation-air drying".(4) Segmentation method is proposed, and the mechanical effect of reservoir rock slope in rising or drawdown of reservoir water levels is analyzed detailed.The variation that the safety factor change from decreasing to increasing along with the change of reservoir water levels are explained by mechanical mechanism, which also can explain some of the reasons for the bank slope instability.(5)The influence of fissure water pressure to the crack intensity factor is analysed in respect of the fracture mechanics. I - II composite crack propagation is studied by considering the fissure water pressure. The results show that the crack propagation angle (?) of composite crack is not only related to the degree of crack closure,the angleαof inclined crack and the size of two-way stress, but is also related to the size of the fissure water pressure and the friction coefficient of the crack surface. In the same circumstances, the propagation angles of non-closed cracks are greater than the propagation angles of closed cracks; and for the closed cracks, the smaller the friction angle, the greater the propagation angle..(6) From the test results of this paper, the effect of simple hydrostatic pressure to water-rock interaction is smaller, the differences is for that the physical and chemical role of water-roc,the rise or decline of water pressure and the role in cycle of "saturation-air dry" has cumulative and magnified effect to the damage of rock. Tests show that the greater the water pressure in immersion, the greater the impact to the ion concentration and secondary porosity, and more development the erosion-corrosion pores. At the same time, the longer of the soaking time, the more cycles of "saturation-air dry", the more serious damage to the rock mass.(7)Based on the change of ion concentration, the computational method of secondary porosity change law in the rock is proposed, which consistent with measured changes of secondary porosity.(8)The microstructure's photographs of the rock samples show that, after cycles of "saturation-air dry" cycles, the mineral particles have undergone varying degrees of dissolution, corrosion, particle boundaries become fuzzy, and irregular shape become smooth, particles of calcium cement tend to be loose, which indicates that the effect of aqueous solution on the sandstone physical and chemical microscopic injury is strong.(9)The morphological characteristics of stress-strain curves of sandstone samples in different soaking times is basically identical, but compacting curve varied greatly in length, as soaking time is the longer, length of compacting would be larger, the slope of the elastic deformation's section became smaller, residual deformation after unloading is increased. The rock samples obviously change soft, and the injury samples which have experienced the cyclic loading and unloading change soft more obviously.(10)In the cycle of "saturation-air dry", longitudinal wave velocity, rebound value, compressive strength, cohesion, friction angle, elastic modulus, deformation modulus of the sandstone samples has varied degrees of deterioration, the change law is consistent basically. Moreover, the greater pressure in the soaking time, the trend is more downward obviously. While the downward trend of strength is related to the confining pressure of the loading test, the lower the confining pressure, the more obviously the downward trend. Compared with the "intact" samples, all parameters of the injury samples deteriorate more severely.(11) With the confining pressure increasing, the elastic modulus and deformation modulus are increased, and changed along with soaking time ("saturation-air dry" cycles), the difference gets more obvious. At the same time,tensile failure characteristics of rock samples is gradually weakened, the shear failure characteristics becomes obvious, which transforms from tensile damage to tensile-shear damage, finally changes to shear tensile damage.(12)Statistical laws show that the shear angle of sandstone samples dwindles with the confining pressure increasing; when under the same confining pressure, the shear failure angle is relatively smaller when the water pressure during immersion is greater; as the soaking time ("saturation-air dry" cycles) goes on, shear failure angle of sandstone samples is progressively smaller, which is consistent with the deterioration law of strength parameters of the sandstone sample.(13)Compared with the compressive strength of the "intact" sandstone sample, the damage degree of injury samples which have experienced the cyclic of loading and unloading is more serious, and the mechanical parameters decay faster, it indicated that injury samples is more sensitive to water, the weakening of the mechanical properties is obviously after long-term "saturation-air dry" cycles and it is easier to generate instability problems.(14) The direct shear test of SRM with the different gradations and different moisture content has been carried out, and the relationship is established between c-ωand (?)-ωof SRM with natural gradation and design gradation, which provides a quantitative basis for evaluating weakening degree of c,(?) of landslide under the condition of the reservoir water level fluctuation.(15)The model for numerical analysis is established to calculate, the results are basically consistent with the monitoring data, and the location of plastic zone calculated is very similar to the cracks region found at the edge and centre of the landslide when macro-geological inspection, but the calculation is smaller.The results show that long-time effect of water-rock interaction must be considered; at the same time, rainfall and water level fluctuation are the main factors for accelerating deformation of the landslide, and the variation law of parameters is also worth further studying when SRM on the landslide surface is under "saturation-air dry" cycles.
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