Experimental-Theoretical-Numerical Studies Of Elasto-Plastic And Creep Property Of Sandstone With Hydro-Physico-Chemical Influencing Effects

Underground water is an active component in geological environment. It is a complex chemical solution with kinds of ions, different concentrations and pH values. Even for pure water, its interactions with geo-materials are not only through the concept of effective stress, but also the complicated Hydro-Physico-Chemical (H-P-C) effect. The instability of rock mass is frequently induced by the time-dependent deformations of intact rock and rock joints; meanwhile, underground water is the most active carrier in most of engineering geological disasters. Previous studies have shown that water plays an important role in mechanical behavior of rocks. Therefore, it is important to assess the role of H-P-C effect in microscopic damage mechanism, conventional mechanical behavior and creep characteristics for theory and engineering applications. In this thesis, microscopic investigations on H-P-C damage mechanism and conventional and creep uniaxial compression tests are performed. Based on the test results, the H-P-C damage mechanism is elaborated, and the creep behavior and modeling are discussed. The achievements and conclusions are summarized as follows:1. A series of test and analysis on mineral constituent, porosity, ion concentration and pH values of solution subject to different solutions are conducted. The time-dependent variations of corresponding physical indices are obtained. Microscopy observation and CT scanning are performed on the sandstones after 180 days' water-circulating with different solutions. The evolution characteristics microstructures in sandstones subject to H-P-C effect are discussed. The mechanism of H-P-C damage is investigated from different perspectives and in different scales. An expression of H-P-C damage variable is proposed for sandstone. The predicted damage values from the expression are compared with those obtained from tests.2. Uniaxial compression tests on dry, water-saturated, and chemical solution-saturated sandstones are conducted. The influences of H-P-C effect on strength, deformation, and post-peak behavior are investigated. The effects of ion concentration and pH value on the strength and deformation are assessed. The modified Duncan model is used to describe the mechanical of sandstones with H-P-C effects.3. Uniaxial compression creep tests on dry, water-saturated, and chemical solution-saturated sandstones are conducted. The influence of H-P-C effect on creep behavior is investigated. It is shown that the influences of ion concentration and pH value are significant to creep behavior. The influence of ion concentration is more significant that that of pH value. The creep strain is greater with higher level of acidity or basicity under the same ion concentration, while the creep strain is greater with higher ion concentration under the same pH value.4. By comparing the creep strains of dry, water-saturated, and chemical solution-saturated samples, the component of creep strain due to H-P-C effect is obtained. The dependency of creep strain on H-P-C effect and loading time is investigated; then, the influence of ion concentration on the creep behavior of sandstone is discussed. Based on the classic Burgers creep model, a new creep model, namely, H-P-C Burgers model, for sandstone subject to H-P-C effect is proposed. Genetic algorithm is applied in parameter determination. With the consideration of influence of ion concentration, the model has the ability to reflect the influence of ground water on the rock facilities.5. The H-P-C Burgers model is coded into Abaqus subroutine, and is applied to reproduce the creep behavior in creep tests, which provides feasibility to apply the model into engineering applications.