Study On Three-dimensional Rheological Constitutive And Long-term Strength Of Q₃Undisturbed-loess In Ground Fissure Zone

The Fen-Wei basin can be the most developed area of ground fissures and the associatedgeo-hazard in China and even in the world. Most of ground fissures development in the loessmedium. The physical and mechanics properties and stratigraphic structure of loess provides aunique pregnancy basis for the growth of ground fissures. Studying fracture extension modelin near surface of the concealed ground fissures will be significance of theoretical andpractical for forecasting and early warning and engineering disaster prevention and control. Inthe past, most of the study of ground fissures formation mechanism and fracture extensionmechanism were based on the classical elastic-plastic mechanics and elastic fracturemechanics theory. The numerical simulation and physical model test come to a conclusionthat the concealed ground fissures in the near-surface rupture expansion were counter-inclined,which not agree with the actual profile structure. This will need to consider in the longgeological history process, the creep and the long-term strength mechanism of loess influencethe crack fracture extension model.Based on this, the paper take the ground fissures of Fen-Wei basin as the researchbackground, on the object of Q₃undisturbed-loess which is located in the east of Jin Hutuoexploratory trench wall of Chang an ground fissure （fc1） in Xi’an region, researched onthree-dimensional rheological constitutive and long-term strength of Q₃undisturbed-loess inground fissure belt. First, through the conventional triaxial compression test, revealedcharacteristics of the stress-strain relationship curve and failure mode of Q₃undisturbed-loessin ground fissure belt, and got shear strength values in different variables and the shearstrength parameters. Second, through the triaxial cyclic loading and unloading creep test,analyzed characteristics of the relation test curve of Q₃undisturbed-loess in ground fissurebelt, and based on uniform rheological mechanics theory, obtained the three-dimensionalrheological constitutive model of Q₃undisturbed-loess in ground fissure belt, established theconstitutive equation of the model and identified the model parameters. The last, based on thecreep test results, built the long-term strength curve in forms of "scores-linear" of Q₃undisturbed-loess in ground fissure belt, obtained the long-term strength equation, and then got the long-term strength and the strength parameters.These achievements for study of concealed ground fissures extension model andmechanical mechanism of the theory and numerical simulation, for concealed ground fissuresprediction and the build （structure） of the reasonable avoidance and hazard prevention laid afoundation.