Study On The Triaxial Loading And Unloading Creep Properties Of Fractured Hard Rock

With the implementation of some major rock mass engineering projects such as high slope and large underground caverns projects in recent years, more and more engineering practices show that the deformation and failure characteristics of hard rock mass often experience a more obvious ageing process.In view of this, and in combination with National Natural Science Foundation Project "Study on the rheological properties and aging propagated mechanism of hard fractured rock under high residual stress", researches carried out in this paper would use a combination method including testing research, theoretical analysis and numerical simulation. Firstly, On the basis of marble rock mass in Jinping I stage hydropower station and sandstone in C hongqing airport, the fractured rock masses were prepared. Secondly, uniaxial compression tests, triaxial compression tests and triaxial compression creep tests for the fractured rock masses under different loading paths were carried out. The deformation and failure characteristics of fractured rock masses under different compression tests were analyzed. Then, the elements creep models were present based on testing results and the correlation of parameters were analyzed. Thirdly, a creep model for fractured rock masses was present based on damage and fracture mechanics. At last, the creep model was programmed and verified in computer.The main contents of this paper were as follows:① Uniaxial compression and triaxial compression tests were carried out for intact rock and fractured rock masses. Based on the test results, strength, deformation characteristics of intact rock and fractured rock masses were analyzed. Combining with numerical calculation results by using software AUTO DYN, the failure characteristics of fractured rock masses were discussed in detail.② In order to know about the creep properties of intact rock and fractured rock masses, triaxial compression creep experiments under different stress loading paths were carried out on RLW-2000 rock servo controlling rheology testing machine. Based on test results, the influence of step unloading value on the creep characteristics of marble rock, the deformation and failure characteristics of different types of fractured rock masses were discussed in detail.③ Based on the feature of creep curves obtained by triaxial compression creep experiments, the traditional elements model were present for intact rock and fractured rock masses of which the creep stages did not contain the third stage. The parameters of the three-dimensional constitutive model are obtained directed by the least square method. Then the correlations of parameters under different conditions were systematic discussed.④ According to the existing relevant research results, assuming that the crack of the fractured rock mass is not extended in the first and second creep stage, thus the prefabricated crack is regarded as a kind of initial damage and the damage variables are calculated, then the fractured rock mass damage creep constitutive models were put forward by using the equivalent strain and energy equivalent principle, and then compared with laboratory tests results. The relationship between the intact rock and fractured rock mass was established by these fractured rock mass damage creep constitutive models.⑤ According to the results of test and theoretical analysis, and combined with the existing relevant research results at home and abroad, based on the understanding that the deformation and failure of fractured rock mass were greatly influenced by the relationship among the value of stress intensity factor K, subcritical fracture toughness K0 and fracture toughness KC, a numerical calculated method for creep of fractured rock mass was proposed. Then on the basis of finite difference software FLAC2 D, the constitutive model was writed by using FISH language for secondary development. The programmed computation of the creep model for fractured rock mass was achieved. At last, in order to verify the feasibility of the proposed numerical simulation scheme, some single- zone and multi- zone models were established and calculated under constant load by using the creep model, and the deformation and failure characteristics of the models were analyzed.