The Research Of Mechanical Properties And Time-dependent Fracture Mechanisms Of The Layered Rock Under High Stress Conditions

The time-dependent mechanical properties of the layered rock and its fracture evolution mechanical have been one of the major research subjects of rock mechanics field. A large number of instances show that lots of instability and destruction of the layered rock engineering have a time lag, especially in the process of tunnel surrounding rock excavation and unloading under high surrounding stress, it`s needs a long time to adjustment the rock stress so as to achieve a new equilibrium, sometimes even induce a lag rock burst and a big time-dependent deformation, which will cause serious damage to the safety in construction and the long-term stability of engineering. Therefore, the time-dependent mechanical properties and fracture evolution mechanical of layered rock under the condition of high stress need to be a better understanding and research. In view of this, this article bases on the true triaxial test of the quartz-mica schist in Dan Ba engineering and take advantage of the three-dimensional particle discrete element theory, introduced SJ model, PSC model and super unit clump technology, and built a mesoscopic mechanics model which is in accordance with the layered rock properties, then make a research for the mechanical properties and time-dependent fracture of layered rock on different structural plane under different stress state and in different stress paths.In this paper, the research work focuses on the following aspects:1. Based on the damage rate driven by exponential mesoscopic internal stress and the three-dimensional particle discrete element theory, and combining with the PSC model which can describe time-dependent fracture at mesoscopic level and the SJ model which can describe the effect of joint, it puts forward a calculation method that can simulate the time-dependent fracture of layered rock with mesoscopic mechanics. This method can be used to simulate the effect of rock structure surface about the transient and time-dependent fracture of rock. At the same time, combined with the three-dimensional particle discrete element theory and seismic moment tensor theory, it gives a AE calculation method and spatial orientation method. AE calculation method and spatial orientation method.AE is used to simulate of the transient and time-dependent fracture of the rock.2. Based on the three-dimensional particle discrete element theory, and introduced SJ model, PSC model and super unit clump technology, and according to the SEM mineral elements test results of quartz mica schist in Dan-Ba hydropower station, it builds a mesoscopic structure model of layered rock based on the form of mineral granular. According to the ture triaxial transient compression test and the rheological test results and the method used to identify the mesoscopic mechanics parameter of rock, the mesoscopic mechanics parameters about the transient and time-dependent fracture of the quartz mica schist have been determined, and a numerical model of layered rock in time-dependent mesoscopic mechanics have been established.3. Based on the numerical model of layered rock in time-dependent mesoscopic mechanics, It conducts the true triaxial transient mechanics test under the conditions of different joint Angle, researches the effect of structure surface about the transient mechanical characteristics of layered rock and AE characteristics, and discusses the deformation and fracture evolution rule and mesoscopic evolution mechanics of layered rock. The results showed that: The failure mode of Layered rock changed with structural surface Angle. At first, it controlled by the rock itself,then change into controlled by rock, structural surface together, and at last controlled by the rock itself, among them, between 45 ° ~ 75 °, rock failure mode is mainly controlled by structural surface.4. Based on the numerical model of layered rock in time-dependent mesoscopic mechanics, It conducts the true triaxial creep numerical test under the conditions of different joint Angle, researches the effect of structure surface about time-dependent fracture of layered rock and AE characteristics, and discusses the deformation and fracture evolution rule and mesoscopic evolution mechanics of layered rock. The results showed that: With the increase of structural plane Angle, the time-dependent deformation mode of Layered rock changed from attenuation creep into steady state-accelerated creep then become boundary in 45 ° around of structural plane Angle.In attenuation creep type, the smaller structural plane Angle is, the greater the rate of convergence is,and the faster the convergence time become, with the increase of structural plane Angle, the convergence time gradually increase and convergence rate gradually decrease; In accelerated creep types of layered rock,damage time of Layered rock is approximation a "U" shape and when Angle is 45 °, rock mass damage time is long, with the increase of Angle, rock mass damage time gradually reduce, destroy the shortest when Angle is 60 ° or so, with the increase of Angle continues rock damage time gradually increase.