Fracture Damage Mechanism And Stability Analysis Of Unloading Rock Mass

With the rapid development of economy in our country,landslides,collapses and other incidents caused by various kinds of infrastructure construction in mountainous areas occur frequently,causing serious harm,it posed a great threat to the safety of people's lives and property and the safety of engineering construction.Since the reform and opening up,rapid development hydropower in our country.In the process of hydropower engineering construction,a large number of high slopes are often formed,due to the excavation of shallow rock mass.Excavation has deteriorated the strength and quality of the rock mass slope,and changed the structure and load conditions of the slope rock mass,it is one of the important factors to induce a large number of slope instability.For the stability problem of unloading rock mass slope,in this paper,the right abutment slope of Rumei hydropower station is taked as a case study.The purpose of this paper is to explore the fracture damage mechanism of unloading rock mass and analyze the stability of unloading slope.After a detailed understanding of topography,formation lithology,geological structure and weathering characteristics in the study area,by used numerical simulation,the purpose of this paper is to carry out the research work of unloading stress,distribution of microcracks,rock mass macro damage factors of associated with the distribution of fine-scale microcracks,and formation simulation of integral fracture zone of slope.The theoretical results and engineering conclusions obtained are as follows:(1)Builded discrete element slope numerical model based on PFC2 D.Carried out simulation test of excavation by stages in slope model.The results show that the number of microcracks and the change of unloading stress in the characterization element of particle aggregation at the monitoring point are larger in the first two stages than in the last two.It shows that the excavation in the first two stages has great influence in the whole slope.Through statistical analysis and test results,the quantitative relationship between the amount of change of micro unloading stress and the amount of change of macro damage factor is obtained.The quantitative evaluation of stress change and rock fracture degree after rock slope excavation and unloading is obtained.(2)Carried out the numerical simulation test of crack growth in unloading slope based on ABAQUS.The results show that the potential sliding surface of the unloading slope is rock bridge failure at no.2 and no.3 low dip fault and cut out from no.3 low dip fault at the shear outlet of excavation face.According to the contour map of damage factor variation distribution,the damage degree of the area nearby of the excavation surface and the fault tip is large.There is a high possibility of fracture failure in these area.Carried out numerical simulation tests of fracture and instability of unloading slope based on ABAQUS and PFC2 D.The result of finite element ABAQUS numerical simulation is basically consistent with the predicted result of the slope,and finally that the slope would occur the slipping-tensile fracture instability along No.2 and No.3 faults.The results of discrete element PFC2 D numerical simulation show that the main failure mode is tension failure in the slope model.It is speculated that the slope would eventually occur slipping-tensile fracture instability at the macro level.(3)Carried out uniaxial compression numerical simulation test based on PFC2 D,aim to calibrate meso parameters.Continuously debug the micro parameters,when it is the best micro parameters.The results show that the stress-strain curves are basically consistent,and the relative error of the basic physical and mechanical parameters is very small,and the failure modes are basically consistent of uniaxial compression numerical simulation test and indoor uniaxial compression test of rock material.(4)Carried out triaxial compression numerical simulation test and triaxial unloading numerical simulation test based on PFC2 D.The results show that the stress-strain curves of the numerical simulation test and the indoor test are basically consistent in the pre peak stage.In the post peak stage,triaxial compression numerical simulation test shows obvious brittleness characteristics,and triaxial unloading numerical simulation test shows strain softening phenomenon.The results show that the relative errors of peak strength and modulus of elasticity of numerical simulation test and indoor test are all very small.The results show that the rock samples finally occurs shear fracture in the numerical simulation test.