Study On Sandstone Rheological Tests And Their Factors Analysis

Under the action of external load, rock shows not only elasticity and plasticity, but also rheological characteristics which are related with time. Rock rheological phenomenon can be observed everywhere in the engineering practice, and rock damage caused by rheology can not be ignored. For example, after tunnel, mine chamber excavation, the surrounding rock may cause deformation or even damage. The foundation of buildings may settle with time, and eventually lead to the buildings damage. A lot of researches on rheological properties of rock are made, and abundant research results have been achieved. However, as a special kind of engineering material, rock’s rheological properties are affected by many factors including the nature of rock(such as mineral component, joints, etc) and the external geological environments(humidity, geostress etc). Therefore, the rock rheological theories are still not very mature so far. In order to predict the long-term stability of rock engineering in complex stress environments, triaxial and shear rheological experiments of sandstones were carried out using the YSJ-01-00 triaxial testing manchine and YZJL-300 direct shear rheometer. Based on the experimental results, theoretical analysis and numerical simulation are developed. The relationship among lithology, confining pressure, axial pressure, moisture content, and crack length with the creep characteristics are investigated. Specific research contents and conclusions are as follows:(1) Based on uniaxial and triaxial compression tests, the uniaxial compressive strength, cohesion and internal frictional angle of fine and coarse sandstones have been obtained.(2) Through triaxial compression rheological experiments, the creep laws of fine and coarse sandstones had been summarized. When axial stress increases, the triaxial compression creep curves of fine sandstones can be divided into two phases including deceleration and constant rheology. The triaxial compression creep curves of coarse sandstones can be divided into three stages including deceleration, constant and accelerated rheology. Due to timeliness, the long-term strength of sandstones have some reduction. The long-term cohesion of fine sandstones decreased over time, but internal frictional angle changed little. The long-term cohesion and internal frictional angle of coarse sandstones decreased with time. The effect of water content upon creep characteristic of coarse sandstones are studied. The higher water content is, instantaneous deformation and creep rate are higher, the long-term strength is lower. The instantaneous deformation has a linear relation with moisture. The long-term strength has a logarithmic relation with the moisture.(3) Through shear rheological experiments the creep law of intact and pre-cracked sandstones are obtained. The long-term shear strength of the sandstones increases with normal stress. The shear fracture surface is smoother, and closer to the pre-cracked plane. When shear stress increases, the shear creep curves of the coarse sandstones can be divided into three stages including deceleration, constant and accelerated rheology. The long-term shear strength decreases rapidly with increase of crack length.(4) Cvisc rheological model is used to fit the rheological test curves, and the constitutive relationships of Cvisc model and its parameters are obtained. The Cvisc model is used for numerical calculation. And the sandstone creep law of the triaxial compression was simulated. The numerical results fit well with the experimental results, which verifies the model describing creep properties of sandstones is useful. The research is applied to settlement of sandstone foundation under building additional stress. The creep rate of foundation is small under low stress, and quickly reduces to zero. Under the conditions of high stress, the creep rate of foundation decreases, then is kept constant. The foundation deformation increases gradually over time.