Study On The Damage Evolution Law Of Limestone In Wuxia Section Of Three Gorges Reservoir Area Under Water-Rock Interaction

There is always continuous physical,chemical and mechanical interactions between rock mass and surrounding water solutions in nature,which inevitably makes changes on the physical and mechanical properties of rock mass,thus leaving a huge threat to the safety of geotechnical structures like crags,slide slops,dam foundations and so on.This appears far more noticeable in Northwest China where is covered by numerous high and steep slopes.A systematic water-rock interaction study is a basic yet significantly meaningful project that contributes to enhance the safety of geometrical engineering in China and reduce the possibilities of related geological disasters.Thanks to the funding support from National Joint Engineering Research Centre of Geohazards Prevention in the Reservoir,and the Science Foundation for Excellent Young Scholars(Overseas)Supported Program,this thesis investigated the law of micro-and macro-scale mechanical property change of Bank slope microcrystalline limestones that extracted from Wuxia Section of Three Gorges Reservoir Area,under dry-wet cycles or long-term immersion,as well as that under the combined conditions.The main contents are as follows:(1)Uniaxial compression and Brazil splitting tests were performed on micrite limestone under different numbers of dry-wet cycles and long-term immersion with various p H,based on which the influences law of dry-wet cycles and long-term acidic solution immersion on the mechanical properties as well as the deterioration mechanisms of micrite limestone due to water-rock interaction were analyzed.Afterwards,analysis about the impacts of dry-wet cycles and long-term acidic solution immersion on the uniaxial compressive strength,Young' modulus and tensile strength of micrite limestone were also discussed.Meanwhile,the degradation of mechanical parameters with respect to the number of dry-wet cycles as well as the time of long-term immersion were quantitatively studied.(2)Based on the Scanning Electron Microscope(SEM)tests,the change law of surface miscrostructures of micrite rocks after varied dry-wet cycles and long-term acidic solution immersion were analyzed,which provided a micro-perspective to reveal the damage mechanisms of micrite limestone due to water-rock interaction.(3)Based on the micrite limestone tests under dry-wet cycles and long-term immersion,the relationship between the mechanical parameters and the number of drywet cycles,n,as well as the time of long-term immersion t,was determined.So did the relationship of deteriorative degree D,and these two parameters.Afterward,mechanical property tests of micrite limestone under combined dry-wet cycles and long-term immersion were conducted.Through introducing a coupling coefficient k,the deteriorative relationship under the combined effect of dry-wet cycles and long-term immersion was established.(4)Based on the tests with varied water-rock interactions and Weibull distribution hypothesis on the rock microelement strength,a statistical damage degradation model was proposed by means of statistical analysis,Lemaitre strain equivalence hypothesis and Continuous damage theory.This model successfully incorporated the influences of number of dry-wet cycles,degrees of acidic solution in long-term immersion and their combined effect,and was verified by comparing against the test results.(5)Limestone specimens with natural soft interlayer were prepared.The mineral composition and microstructure morphology were firstly analyzed based on energy spectrum and SEM tests.Shear tests on respective complete limestone specimens and that with natural soft interlayer were conducted under dry-wet cycles,to analyze the impact of dry-wet cycles on the strength of both complete limestone and that with soft interlayer.The influence of soft interlayer on the degradation of limestone was also discussed in drywet cycles cases.Based on the change law of cohesion and internal friction angle under varied numbers of dry-wet cycles,the degradative model for limestone was developed.(6)Based on degradative law of macro-scale mechanical parameters of micrite limestone under water-rock interaction,three-dimensional discrete element models for water-induced strength degradation prediction were proposed.The characters of microscale parameters of micrite limestone were analyzed under dry-wet cycles and long-term immersion.Meanwhile,by using the relationship of the macro-scale strength parameters under dry-wet cycles,long-term immersion and the combined conditions,a micro-scale degradative model for the combined cases was proposed,based on which the degradative law of micrite rocks due to the combined effect was discussed.