Study On The Water Damage Evolution Model Of Gypsum Breccia And Its Mechanical Properties

Gypsum breccia is a type of water-sensitive rock rich in clay. The strength of gypsum breccia decreases rapidly while meeting water, which is critical to the design, construction and maintenance of relevant projects.Based on the strength and swelling tests, the swelling characteristics and the mechanical properties of this rock are investigated. The microcosmic mechanism of Water-Rock Interaction(WRI) in gypsum breccia is addressed through microscopic observation. The main research contents are listed as follows:According to the swelling test, the change patterns between the swelling stress and the strain of gypsum breccia are obtained, and the improved Hunder-Amberg model is proposed. After that, a constitutive law describing one-dimensional unstable expansion is established by introducing the time factor.By the uniaxial and triaxial compression tests, the stress-strain curve, the deformation and strength parameters of gypsum breccia with different initial water contents and different confining pressures are determined, and the change patterns are generalized. The effect of the water content on the brittle-ductile transformation is analyzed.With the micro-measurement methods, SEM and XRD, the existing forms of water molecules, that have an influence on the microstructure in gypsum breccia is studied. The mechanism of water-rock interaction is analyzed in the mechanics, physics and chemistry ways. Last, a water damage model is developed.From the above results, the re-definition of the free energy and the specific free energy and the introduction of water damage, based on thermodynamics and continuum damage mechanics, the elastic-plastic constitutive model of gypsum breccia considering expansion and damage, are given. Using this model proposed, the rock stress-strain curve after the peak can be simulated well.To sum up, the swelling characteristics and the mechanical properties of gypsum breccia are detailedly studied through experiments. The swelling models and the water damage model are established. After the free energy and the specific free energy are re-defined in theory, the elastic-plastic constitutive model of gypsum breccia considering expansion and damage are built. The results obtained here are also applicable to water-sensitive rocks which characteristics are similar to gypsum breccia.