Study On Macro-meso Damage Characteristics Of Argillaceous Sandstone Under Dry-wet Cycle In Acidic Condition

Groundwater have mechanical,physical,and chemical effect on the rock mass.Water-rock interaction is one of the most basic subjects in geotechnical engineeringsuch as side slopes, perilous rock,dam foundation, protection of cultural relics, et al.Studying the issues have very important significance. With China’s intensifiedexploitation on water power and hydroelectric resources, more and more reservoirs areconstructed. As a consequence, geological environment and hydrological condition inreservoir area are faced with unprecedented changes. The strength of rock and soil massin side slope of reservoir bank may deteriorate under the effect of dry-wet cycle andacid environment. When the deterioration reaches certain degree, the bank slopebecomes unstable. With regard to this problem, the paper firstly summarized theresearch findings of predecessors, and then performed a mechanical test to determinethe stability of argillaceous sandstone when it is affected by different times of dry-wetcycle and saturated by acid solution. Supported by “the Research Fund of Ministry ofEducation for the Doctoral Program of Higher Education with the theme ofMacroscopic and Microscopic Research on the Damage Mechanism of RockDeterioration under the Effect of Dry-wet Cycle”. Main research activities andbeneficial findings obtained are described as follows:1) Argillaceous sandstone hygroscopic property test, uniaxial and triaxialcompression test, as well as tensile test are performed under different times of dry-wetcycle and acid solution erosion conditions, so as to analyze the influence of dry-wetcycle and acid solution soaking on the microscopic structure of argillaceous sandstone,and to discuss water-rock damage mechanism of argillaceous sandstone. On this basis,the influence rule of dry-wet cycle and acid solution on uniaxial compression strength,elasticity modulus, cohesion and internal friction angle of argillaceous sandstone isanalyzed as well. On the other hand, rock parameter deterioration function under theeffect of dry-wet cycle is introduced to quantitatively describe the changing process ofargillaceous sandstone mechanical strength under different times of dry-wet cycle inacid and neutral environment.2) Based on the test, according to related theories in elastic-plastic mechanics, andtaking into consideration the strain softening of rock, a four-segment model comprisedby linear elasticity, Duncan hyperbolic curve, plastic softening and residual ideal plasticity is constructed, and the constitutive equation is established by segment.Applying the continuum damage mechanics and statistics theory and on the premise ofWeibull distribution, argillaceous sandstone damage statistical constitutive model isestablished, which separately takes M-C, D-P and H-B strength criterions as themeasurement for rock material microelement strength.And it is better to match withexperimental results.3) In accordance with the dry-wet cycle test result, assuming that the rockmicroelement strength is subject to Weibull distribution, taking advantage of thehypotheses of continuum damage theory, statistical method, and Lemaitre strainequivalent, based on D-P strength criterion and Hooke’s law, rock damage statisticalconstitutive models under dry-wet cycle process in acid and neutral environment areseparately constructed, so as to analyze the influence mechanism of dry-wet cycle ofacid and neutral solution on the mechanical property of argillaceous sandstone. Theresults showed that,most cases are in good agreement with the experimental results.4) When applying scanning electron microscope and energy spectrum analysis tostudy the microstructure and mineral composition of rock, and studying on themechanical properties of argillaceous sandstone mechanism under dry-wet cycle inacid environment,it is found that, affected by the dry-wet cycle of water physical andchemical solution, the mineral composition and microstructure of argillaceous sandstonemay incur changes. As for this, particle flow code numerical simulation software isadopted to simulate and analyze the microscopic damage on argillaceous sandstone. Themicroscopic parameter changing rule of argillaceous sandstone under the effect ofdry-wet cycle is explored. The relation between microscopic parameter and the times ofdry-wet cycle is analyzed. Moreover, dry-wet cycle microscopic parameter deteriorationexpression is defined, which is designed to quantitatively describe the influence degreeof dry-wet cycle on microscopic parameter of sandstone.5) Shown by the calculation and analysis on microscopic model, particle contactnetwork bearing the same ambient pressure under peak stress state has similardistribution pattern with particle force chain. However, there is difference in thicknessand distribution of force chain. The number of breakage in cohesion between particlesincreases along with the growth of dry-wet cycle times. Furthermore, fissures tend tobecome similar as well. Under the acid condition, the number of breakage in particlecontact network is much larger than that under the neutral condition. What’s more, theamount of shearing fissures inside the test sample also increases considerably. In order to analyze the microscopic fissure of particle, an argillaceous sandstone microscopicdamage model based on microscopic modulus is constructed. Based on the test andresearch, the microscopic deterioration process of argillaceous sandstone is analyzed,and the microscopic damage mechanism of argillaceous sandstone under the effect ofdry-wet cycle is explored and discussed. And it provide theoretical basis of argillaceoussandstone macroscopic damage under dry wet cycle in acid environment.