Siltstone’s Mechanical Properties In Different Stress Paths And Research Of Unloading Constitutive Model

The excavation of underground engineering rock mass, in essence, is a process of unloading. Using, without any distinction, the relative theories and methods of loading rock mechanics to the design, construction and stability analysis of excavation engineering with obvious characteristics of unloading may results great deviations. In order to deeply study the deformation characteristics, ultimate bearing capacity and failure properties of rock mass in different loading and unloading stress paths, this article, through selecting typical siltstone specimen, separately conducts laboratory triaxial compression tests and four stress paths’ unloading confining pressure tests in the condition of axial compression is constant, axial compression is improved, deviation stress is constant and axial displacement is constant; simulates a varirty of possible stress adjustment paths in the process of excavating unloading; comparativly analyzes the differences of rock-mass’ s mechanic properties such as deformation, failure and so on in loading and unloading condition; studies the influence of stress path to unloading rock-mass’ s mechanic properties. In the process of experiments, through changing the unloading confining pressure rate, the paper also separately studies the influence of unloading confining pressure rate to rock-mass’ s mechanic properties in different stress paths. Besides, through going on Micro-scanning electron microscope to fracture surface after sampling, analyzes the micro characteristics of fracture surface in different loading and unloading stress paths and unloading confining pressure rate. According to the test results, analyze and evaluate several widely used rock strength criterion. Based on elastic-plastic mechanics, compared with Hoek-Blown strength criterion and Griffith strength criterion, derive rock-mass unloading institutive model that fits in with the results of tests. The research results have some theoretical and practical value.