Experimental Study On Rock Mass Rheological Properties And Identification For The Constitutive Model And Parameters

For the rock underground engineering, construction base, slope and landslide, rock rheology is one of the important reasons for the large deformation and loss of stability. So it possesses important theoretical significance and practical value to rationally describe and reveal the time-dependent mechanical characterization and behavior of rock mass, to understand of the time effect deformation and failure characterization. With a series of important and great projects such as Three Gorges Project, Shuibuya Project, Goupitan Project, Jinping Project etc as engineering background, the paper aims at the time-dependent deformation behavior and the long term stability of rock engineering. Experimental study on the creep characterization of rock mass and the structure plane of different scales. Based on the creep test results and the measuring displacement in situ, the rheological constitutive model and parameters identification method is discussed. The main research work containing some aspects as following:(1) In concert with the designing of Qingjiang Shuibuya hydroelectric station Maya high slope and Wujiang Goupitan hydroelectric station underground powerhouse, representative soft rock and hard rock in the slope and underground cavity surrounding rock are selected as the research objects. The creep behavior of different types of rock is studied through laboratory uniaxial compression creep test.(2) Considering the fact that complex rheological models with too many parameters are rarely adopted by practical engineering, the component-combined model is selected for its simplicity and convenience and the good performance to represent the main deformation behavior of rock mass. The rheological model parameters identification method is discussed based on the laboratory creep test results. The method makes some improvements on the least-square-based nonlinear function curve fitting. The pattern search optimization method is introduced into the least-square method, so the solution of linear equation set is unnecessary and the difficulties in the selection of initial values for the model parameters is effectively avoided. The practical engineering examples show that the computational accuracy is high and the parameters identification is convenient, so the method has considerable practical value.(3) With the hard structure plane that extensively distributed in the hard rock as research object, it is the first time to perform laboratory and in situ shear creep experimental study on the hard structure plane with no filling. Some understanding of the shear creep behavior and the deformation failure characterization of the structure plane specimen with different sizes is obtained. The creep model to discribe the shear behavior of hard structural plane is established bases on the experimental results, and so is the relationship between the stress level and the model parameters.(4) Rock mass is distinguished from rock as a continuum for its structural specialty, it is this structural specialty has a strong influence on the mechanical behavior of rock mass, and plays a controlling role. The creep mechanical effect of the rock mass structure is performed through computer simulation test. Through uniaxial and triaxial compression creep computational modeling experiments on homogeneous rock mass and structure plane specimen with different distributing occurrence and amount, the structure effect and the peripheral pressure effect on the rock mass creep are discussed, so are the creep deformation behavior and the failure characterization under different structure conditions.