The Experiment Study On The Uniaxial Loading And Unloading Creep Characteristics Of The Red Sandstone

Rheological behavior of the rock is closely related to the long-term stability ofthe rock mass. The laboratory test and numerical simulation are the main methods to study rheological properties of the rock. With the large infrastructure construction, for example,the fortes deep-buried tunnel, the high and steep rock slope, the nuclear waste disposal repository and the underground power housein our country, the stress of surrounding rocksof underground buildings in the project lifecycleis complicated and changeable.The safety during the project construction and the long-term stability in the project operation periodof underground buildings relate to the success of project construction and the national economy and the people’s livelihood. Therefore, it is significant to carry out a research of rock rheological properties under complex stress states.This paper is based on the science and technology project in Jiangxi province(NO.20123BBG70214) “the experimental study of rheological characteristics of rocks under complex stress states”, an expressway tunnel of the Poyang Lake Ecological Economic Zone in Jiangxi province as the engineering background.The author has taken the creep experimentof the typical red sandstone of the Poyang Lake Ecological Economic Zone in Jiangxi provinceunder uniaxial loading and unloading conditions, and the author has exploredrheological mechanical properties under uniaxial loading and unloading stress state with laboratory experiment and numerical simulation,two kinds of test methods, and established the constitutive model of uniaxial creep of red sandstone under theloading and unloading condition. The author has made a numerical simulation of the creep experiment with the same condition of indoor experiment by invoking the creep constitutive model established from indoor experiment in the finite difference software FLAC3 D.The main work and research results of this paper are as follows:(1) The typical red sandstones were acquired from anexpressway tunnel face of the Poyang Lake Ecological Economic Zone in Jiangxi Province, and were processed into standard specimens in the indoor rock slice lab room.The uniaxial compressive strength of red sandstone, the uniaxial tensile strength, elastic modulus, Poisson’s ratio, angle of internal friction and cohesion corresponding basic mechanical parameters were obtained bythe uniaxial compression test, the uniaxial direct tensile test and direct shear test of red sandstone specimens.(2) The uniaxial creep experiment of red sandstonespecimens were carried out byusing multi-step incremental cycling loading unloading loading. Studies have shown that the long-term compressive strength of red sandstone was 80% to 90% of the instantaneous uniaxial compressive strength; as with the analysis of the uniaxial creep experiment curve, it was found that the creep curves of red sandstone hadthe decay creep, steady creep and accelerated creep three typical stages; creep deformation of red sandstone had complex visco-elastic-plastic coexistence characteristics by the visco-elastic-plastic characteristic analysis of the creep strain of red sandstone.(3) The basic elements and their combination in the creep constitutive model of red sandstone were acquired by the analysis of uniaxial creep experiment curves, and Burger’s model based on Mohr-Coulomb yield criterion was established to reflect the threecreepstages, also known as the Cviscmodel; the nonlinear least squares algorithm,the Levenberg-Marquardt method was employed to fit the uniaxial creep experiment curvesin terms of creep equation, and the creep parameters under the different stress conditions were acquired. The research showed that the fitting curves were in good agreement with the experimental curves, which fully certained that the Cvisc model could well reflect the creep characteristics of red sandstone under the uniaxial loading and unloading stress state.(4) The basic principle of FLAC3 D software, advantages and disadvantages and the creep calculation methodwere briefly introduced in this paper. The numerical analysis of uniaxial loading and unloading creep experiment of red sandstone by selecting built-in Cvisc model in the software and using the same physical and mechanical parameters asthe indoor uniaxial creep experiment. After comparative analysis, it was proved that the creep constitutive model was correct.