Macro-Mesomechanical Experiment and Theoretical Analysis on Limestone under Coupled Chemical Corrosion and Water Pressure
|School||Wuhan Institute of Rock and Soil Mechanics|
|Keywords||limestone chemical solution corrosion pore pressure neural network constitutive model fracturing progress cellular automata theory|
Groundwater have mechanical, physical, and chemical effect on the rock mass. Water-rock interaction is one of the most basic subjects in rock and soil engineering such as side slopes, dam foundation, chamber, petroleum drilling, geothermal development, nucleus wastes treatment, energy storage underground, CO2 storage underground, protection of cultural relics, et al. Studying the issues have very important significance. Aiming at these problems above, a set of macro-mesomechanical experiments on limestone under coupled chemical corrosion and water pressure was carried out; An evolutionary neural network constitutive model is proposed to describe the whole stress-strain process of rock under chemical corrosion and confining pressure. The action mechanism of chemical solution and water pressure on limestone is analyzed. Based on the cellular automata theory, the fracturing progress of pre-existing flaws limestone is simulated. In sum, the main work and conclusions including:1. The triaxial compression test of hard brittle limestone with chemical corrosion was carried out, and the effect of chemical solution on mechanical behavior of limestone is studied. The variety regulation of strength and deformation parameters are investigated. The change regulation of ion concentration of chemical solution is gained, and the mechanism of chemical corrosion on rock mechanics property is analyzed. The experimental results indicate that: Chemical corrosion results in the transformation of brittle failure to ductile failure of rock; The cohesive force c、internal friction angleφand modulus of elasticity E are reduced, while the Poisson’s ratiosυincreased. The degradation of strength and deformation parameters is related to the variety of mineral amount: the great the ion concentration dissolved from the specimens, the great degradation of mechanical parameters.2. The results of triaxial compression tests indicate that, the factors influencing on rock’s mechanical properties includes mechanical and chemical aspects: mechanical factors dependent on stress history and confining pressure, chemical factors dependent on water-rock interactions. Based on the study above, An evolutionary neural network constitutive model is proposed to describe the whole stress-strain process of rock under chemical corrosion and confining pressure, and the model have good result of forecasting.3. Experiments of pre-existing flaws limestone fracturing process are conduced under uniaxial compression in order to investigated the behavior of rock fracturing under chemical corrosion and water pressure with a new meso-mechanical testing system. The stress-strain curves corresponding meso-fracturing pictures of rock is recorded. The researches indicate that: under chemical corrosion and water pressure, the crack propagation and coalescence manner changes, and the fracturing behavior become more complicated.4. The action mechanism of chemical solution and water pressure on limestone’s fracturing behavior is analyzed. It is found that the micro-structure and mineral composition have changed at different degree under chemical corrosion by X-ray diffraction, SEM, energy spectrum analysis, et al. The variation regularity of pH value and ion concentration is gained by water analysis. Basic on experimental and theoretical analysis, the interpretation about the effect of chemical solutions on rock fracturing behavior focuses on two different aspects: reduction of rock’s mechanical parameters, and increasing rock’s heterogeneity. The splitting and squeezing effect of chemical solution are favorable to crack propagation. Pore pressure have different influence on rock at different stages of the crack propagation.5. Based on the cellular automata theory, the fracturing progress of pre-existing flaws limestone under chemical corrosion is simulated. The chemical influence of mechanical parameters reduction and the heterogeneity increasing on rock fracturing behavior is analyzed.