Study Of Unload Creep Properties Of Rock Under High Confining Pressure And High Water Pore Pressure And Its Engineering Application

Deep tunnels are appeared constantly in the construction of infrastructure, such asQinling tunnel, the water diversion tunnel of Jinpin, the New GuanJiao tunnel of theqinghai-tibet railway etc. Under the condition of high stress and high underground waterpressure, tunnel construction safety problem is increasingly prominent. Under the actionof high ground stress and high water pressure, the mechanics response of cavernsurrounding rock mass is different from the shallow rock mass. The deformation andfailure mechanism of the deep buried tunnel has attracted the attention of experts indomestic and overseas, but the research of the cause is not yet an in-depth. Thus, by theindoor test, the method of combining the theoretical analysis and numerical simulation,This article carry out the systematically research on the unloading characteristic ofsandstone in instantaneous deformation failure, strength and creep under high confiningpressure and high pore water pressure. According to the experimental results, aexperienced Model of Hoek Brown’s parameters and a nonlinear visco-elastoplasticunloading creep constitutive model reflectign the pore water pressure effect arepresented. Finally, take the deep buried tunnel excavation engineering influenced by thedeep karst water as the background, experiment and theoretical research results of thispaper was applied to the numerical analysis by the software FLAC3D. The mainresearch contents and results are as follows:①Through the rigid MTS815servo testing machine, the instantaneous mechanicscharacteristics of a deep sandstone from Chongqing were studied by the test of uniaxialloading, conventional triaxial loading, riding axial–unloading confining pressure andthe fixing axial–unloading confining pressure at different water pore pressure. anew-experienced Model of Hoek Brown’s parameters suitable for unloading of rock waspresented.②By the RLW-2000rock rheology testing machine, the creep characteristic ofsandstone was studied in the process of fixing axial–unloading confining pressure atdifferent water pore pressure.Based on the result, the influence on unloading creep bythe different stress and water pore pressure were analysized. And the research was mailyfocused on the change rule of instantaneous deformation, creep strain, instantaneousdeformation modulus, volume creep strain and the creep rate at the different water porepressure in the fixing axial–unloading confining pressure. ③Through the analysis of change rule of deformation modulus at the visco-elasticstage in fixing axial–unloading confining pressure creep test, a expression ofdeformation modulus changed with water pore pressure and time was presented. Andassume the Hooker of Kelvin can be expressed by this expression, then put thisimproved Kelvin with an another Hooker in series to compose a nonlinear generalizedKelvin model. This model can better describe the high confining pressure high porewater pressure under the action of sandstone viscoelasticity creep property.④Using exponential function to fit the accelerating creep curves in the test offixing axial–unloading confining pressure at the different water pore pressure. And bythe analogy of this fitting result and the liner equation of visco element, a nonlinearelement was obtained. Its viscous coefficient was a function of water pressure and time.Put this nonlinear element with a plastic element in parallel to construct a nonlinearBingham model. The model can describe different accelerated creep property ofsandstone under pore pressure unloading.⑤Connect nonlinear generalized Kelvin and nonlinear Bingham in series toestablish a nonlinear viscoelastic plastic creep model which can reflect creep proportiesunder high confining pressure high water pressure. And according to the creep testresults, the quasi-Newton algorithm based on MATLAB (BFGS algorithm) waschoosed to identify the parameters of creep curves at different pore water under highconfining pressure, the identification effect is ideal.⑥By the Lagrange finite difference theory, this article deduced the the finitedifference form of nonlinear visco-elastic plastic creep the model. Mohr-Coulombyield criterion on basic of the parameters model of Hoek-Brown was adopted to theestablishment a complex non-linear visco-elastic plastic model, and combined withFLAC3Dsecondary development environment the composite model was secondarydeveloped. Finally, It can be verified that the correctness of the secondary modeldevelopment by using the creep test curve and the model simulation experiment.⑦Numerical analysis of the rock surrounding deformation in the excavationconstruction process of deep bury tunnel infuencede by the karst water in southwestwas carried out by using the nonlinear viscoelastic plastic creep model secondarydevelopment application.