Study On Triaxial Creep Mechanism And Creep Model Of Mica-quartzose Schist At Dam Abutment Of Heihe Reservoir

In this paper, aimed at mica-quartzose schist at left dam abutment of heihe reservoir, by using the study method that test study combined with theoretical analysis, macro-scope study combined with micro-scope study, the creep characteristics and creep mechanism of mica-quartzose sschist are analyzed, the creep constitution models are alse established on the basis of triaxial creep tests, polarization microscope analysis and scanning electron microscope analysis.Firstly, triaxial compression creep tests with mica-quartzose schist which is a kind of soft metamorphic rock with lots of schistosity surfaces were carried out on the rock servo-controlling rheology testing machine under the condition of the axial stress vertical to the direction of the schistosity surface. Axial creep characteristics of mica-quartzose schist were analyzed by comparing with radial creep characteristics. It was proposed that, for the mica-quartzose schist, taking the long-term strength of radial creep as the long-term strength was more reasonable since the radial creep is more sensitive than the axial creep. Besides, the higher confining compression is, the stronger the restrain of compression was to radial deformation, which resulted in increase of both the long-term strength of radial creep and the long-term strength axial creep. However, the ratio of the long-term strength of radial creep to the long-term strength axial creep reduces with increased confining compression, therefore, the long-term strength of axial creep can be taken as the long-term strength when studying the uniaxial creep characteristics. The test results alse show that the schistosity surfaces have little influence on the creep characteristic of mica-quartzose schist and it can not control the creep of mica-quartzose. The characteristics of radial isochrounous stress-strain curve and axial isochrounous stress-strain curve are concluded, which shows that the creep of mica-quartzose schist has apparent nonlinesrity. Three kinds of axial creep rate-time surves and radial creep rate-time curves with the related three kinds of viscous coefficient-time curves have been summarized as well, furthermore, it proposes that the radical reasons of the component-combined creep model can not describe the speedup creep phase are that they can not reflect the true variation regularity of viscosity coefficient.Secondly, mica-quartzose schist is separated as defaults such as pores and cracks, relative rigid part and relative rigid soft which are altogether three parts on the basis of polarization microscope analysis and scanning electron microscope analysis of both axial and radial strip of mica-quartzose schist at different creep stage, at the same time, four kinds of microstructure change which are the close of open crack, the situation change of relative rigid part, the situation change of relative soft part and micro-cracking are put forward. Micro-creep mechanism of mica-quartzose schist is investigated, the reasonable interpretations of micro-mechanism on the initial attenuation creep phase , the stabilization creep phase and the speedup creep phase are put forward. The influence of microstructure change on mica-quartzose schist are summarized as the damage effect and the change of porosity, the relation between the macro-mechanics variable and microstructure change is established indirectly through establishing the relation of macro-stress and macro-strain with porosity and damage variable.Thirdly, seven-component linear viscoelastoplastic creep model and nonlinear viscoelastoplastic creep model of mica-quartzose schist are established. By using a same model, the model parameters of axial creep and radial creep are fitted in accordance with test curves and the comparison between the test curves and fitted curves shows that the creep model is right and reasonable. The influence of compression to model parameters and the different between axial model parameters and radial model parameters are also studied by comparing the average of every model parameters. The factors which influence the model parameters during in the course of fitting are summarized, and a comprehensive identification method to select model parameters is put forward.Finally, a creep damage variable which has two model parameters and can reflect both the creep mechanism and four microstructure change of creep is defined. After simplified and separated, this creep damage variable can reflect the change of viscosity coefficientη₃ with time not only under destroyed stress level but also under middle and high stress level. A damage creep constitutional model is obtained by considering the effect of damage and creep, and the comparison between the test curves and fitted curves shows that the creep model is right and reasonable. The model parameters are also determined, and the sensitivity of model parameters is analyzed.