Research On The Influence Of Water On The Instantaneous Srength And Time-Dependent Deformation And Failure Of Granite

With the rapid development of rock engineering construction,the stability of rockengineering has been paid more and more attention,and Creep is one of the important factors affecting the stability of rock mass.When rocks are subjected to lower stress level,creep will occur,while creep in water environment is more obvious.This phenomenon will directly affect the function and use of engineering,such as the time-dependent problem of rock engineering,the selection of surrounding rock of nuclear waste disposal bank and the monitoring of roof in the hollow area,and so on.Therefore,it is necessary to further explore the creep behavior of rocks in different water-bearing states and try to reveal the characteristics of rock creep behavior from different angels.In this paper,laboratory experiments and theoretical constitutive analysis will be carried out.The basic mechanical parameters of granite and uniaxial creep behavior of granite under different combination of water and stress conditions are obtained through experimental study;and a new nonlinear creep model is constructed by theoretical constitutive analysis.The experimental data of uniaxial creep are used to fit the parameters,and experimental creep curves and the fitting curve of the model are verified.(1)Before studying the creep characteristics of rock,the water absorption experiment was designed on the existing the granite rock samples,the water content curve was obtained,and the instantaneous mechanical properties of rock was tested under uniaxial compression and indirect tensile with moisture water content of granite.Thus,the basic mechanical parameters of granite are obstained.The results show that the tensile strength and compressive strength of granite decrease gradually with the increase of moisture content,and the elastic modulus decreases obviously at the early stage of the increase of moisture content,then tends to stabilize,and the peak strain decreases gradually,and the failure morphology is obviously different.The compressive strength of granite decreased after the same moisture content was sealed for two days,indicating the influence of the distribution of water position on the strength of granite.(2)In the uniaxial creep test,the creep tests of granite are carried out in different water bearing states,mainly the creep tests of granite are under natural,dry,force-water,water-force,and soakingand sealed.Through the analysis of the creep curve of granite,it isfound that with the increase that with the increase of the stress level,the creep failure time is shorter,the stable creep strain rate increases,and the accelerated creep stage appears earlier.The creep strain rate of granite under different stress levels is different.Through data analysis,the stable creep strain rate and the accelerated creep strain rate of granite show positive correlation with the stress level.At the same time,the creep curves of granite under different water cut state indicate that the creep of the granite will change rapidly after force-water.This result is different from that of actual engineering.In the past,the long-term stability of rock in water has been estimated too high,which provides a certain reference for future engineering design and construction maintenance.(3)Based on the experimental results of accelerated creep of granite,a nonlinear viscoplastic element is proposed,which is parallel to the existing plastic body,thus a new nonlinear viscoplastic model can be obtained to reflect the stage of rock accelerated creep.Based on Burgers model,a new nonlinear viscoelastic creep model of rock is established based on the nonlinear viscoplastic model and its series connection.The parameters of the creep data of granite are identified,and the creep curve is compared with the fitting curve to verify the accuracy of the model.The results show that the nonlinear creep model can describe the three stages of rock creep well,and fit the creep curve of red sandstone at the same time,which proves that the model has a more extensive applicability.