Research On Rock Creep Tests Under Seepage Flow And Variable Parameters Creep Equation

Many hydraulic projects would serve decades or hundred years, therefore the design and construction of such project must insure its safety during a long service time. Some engineer practice has proved that the creep of rock often plays an important role in the deformation or failure of underground cavern, basement and slope. Recently, rock mass in some domestic hydraulic projects were found to show its creep properties more obviously under seepage flow, which bring some disadvantage influence to the long term stability of project. However, the issue of rock creep under seepage flow has not been studied thoroughly, it's necessary and urgent to improve on test equipment, method and creep theory. So, several rock seepage-creep coupling tests and theory research work have been accomplished in this paper to provide new research idea and method to long term stability problem of rock engineering.Experiments are taken as foundation of whole research work in this paper, the theory and numeric simulation of rock creep are developed base on test results. Firstly, an effectual experiment system and method of rock seepage-creep coupling test are developed by the improvement of existing equipments. 5 coupling tests have been done by 2 test schemes using porous limestone as specimen. Main rock creep properties under seepage flow are investigated by test results, including the influence of stress and seepage on rock creep, volume creep and permeability coefficient of rock and their relation, creep rate and creep Poisson's ratio etc.The existing three-dimensional creep equation can not truly reflect the nonlinear character of rock creep due to the adoption of some hypothesis in deduction which conflict with rock creep phenomenon. The variable parameters method is proposed in this paper to improve creep theory, the nonlinear character of entire creep process could be reflected by the nonlinear change of creep parameters. Based on rock seepage-creep coupling test results, each creep parameter at different time under different stress and seepage pressure is figured out by nonlinear least square method, then the expressions of creep parameters vary with stress, time and seepage pressure are put forward by nonlinear curve fitting of creep parameters'distribution, finally form three-dimensional creep equation with variable parameters. The variation rule of creep parameters has been proved to be certain applicable by the analysis of existing creep test results of different rock.The numerical simulation of creep with variable parameters under seepage flow could be achieved through seepage calculation program GeoSeepage and FLAC3D. As an elucidation, the creep of left bank underground cavern of Xiluodu hydropower station is simulated to discuss the long term stability of cavern surrounding rock under seepage flow.