A Rheology Model Incorporated Scale Effect For Rockfill And Its Engineering Application

Rockfill material is an aggregation of rock granules. It is widely used in concrete face rockfill dam, core wall rockfill dam and roadbed. Long-term deformation of rockfill is time dependent. Test and engineering observation data show that rheological behavior of rockfill is obvious after loading. On the other hand, macroscopic rheological behavior of rockfill has scale effect and it is affected by physical property, geometry form, size and arrangement of the internal rock granules. Rheology models in classical continua theory were unable to incorporate scale effect for rockfill due to the independence on scale. Micropolar continua theory with the internal length scale provides a possible approach to incorporate scale effect. A Perzyna's viscoplastic model is developed based on micropolar continua theory to investigate the scale effect and stress dependency on rheology for rockfill. The major contents in this dissertation are as follows:(1) The method of considering scale effect of rockfill based on micropolar continua theory is researched. The physical interpretations of size, roundness, sphericity and roughness of particles are analysed. The internal length scale in micropolar continua theory is used to incorporate the sphericity index, roundness index, and mean diameter of the particle. Several mathematical expressions of the internal length scale are given to adapt different using conditions.(2) The graduation, compactability, nonlinear strength, dilatancy and wet property of rockfill are introduced for choosing and developing the constitutive models of rockfill.(3) The typical nonlinear constitutive models of rockfill are researched and own opinions for Duncan-Chang model, modified Duncan-Chang model, south water model, K-G model and Ym's model are explained.(4) The stress dependency, scale effect and loading stage effect of creep of rockfill are studied by uniaxial and triaxial creep tests. Empirical models, component models and general stress-strain-time models are introduced for choosing and developing creep model of rockfill. Meanwhile, own opinions for these models are expounded.(5) A Perzyna's overstress elastic-viscoplastic model is developed based on micropolar continua theory to investigate the scale effect on rheology for rockfill. The consistent operator in the framework of micropolar continua theory is derived based on Drucker-Prager yield criterion. The constitutive integration algorithm and its closed form of the consistent tangent modulus are also acquired. The code is implemented by User-defined elements (UEL) in ABAQUS platform. Triaxial compression creep tests of soft rock rockfill, creep and stress relaxation tests of rockfill, are simulated by finite element method. The results using finite element analysis show a good agreement with the experimental data in literatures, which verifies the adaptability of the model. The creep and stress relaxation test simulations show the advantage of general stress-strain-time models for different boundary conditions. The results show that the pressure-sensitive and the scale effect on rheology for rockfill can be captured.(6) The Duncan-Chang model is developed based on micropolar continua theory to investigate the scale effect for concrete face rockfill dam. The work aims to confirm the initial stress and displacement conditions of creep better. The construction process of Sanbanxi concrete face rockfill dam is simulated by the proposed model. The stress and displacement in completion period are used as initial conditions of creep later. The construction process of Sanbanxi concrete face rockfill dam is simulated by Duncan-Chang model in classical continua theory and the developed Duncan-Chang model in micropolar continua theory respectively. The comparison of the simulation results and engineering observation data verifies the adaptability of the models. The results show that the vertical displacement by Duncan-Chang model in classical continua theory is smaller than the engineering observation data, and the the vertical displacement by developed Duncan-Chang model in micropolar continua theory is more accurate. Furthermore, the scale effect law of the rockfill for the instantaneous deformation is given based on the relationship between the maximum vertical displacement and the internal length scale.(7) A Perzyna's overstress elastic-viscoplastic model is developed based on micropolar continua theory to investigate the scale effect on creep for concrete face rockfill dam. The stress and displacement in completion period of Sanbanxi concrete face rockfill dam are used as initial conditions of creep. The parameters from lab tests and engineering observation are used in the micropolar elastic-viscoplastic model to simulate the creep behaviors of Sanbanxi concrete face rockfill dam in 2000 days after completion. The results show that the vertical displacement, the major principal stress and the minimum principal stress increase after completion. However, the increase rates decrease. The comparison of the simulation results from lab tests parameters and engineering observation parameters shows that the vertical displacement and the major principal stress from lab tests parameters is smaller than the results from engineering observation parameters. The scale effect on creep for concrete face rockfill dam can be characterized by tunning the internal length scale. Furthermore, the scale effect law of the rockfill for the creep deformation is given based on the relationship between the vertical displacement at the top of the dam and the internal length scale.The stress dependency of creep for rockfill can be described by the proposed elastic-viscoplastic model based on micropolar continua theory. The results using finite element analysis show a good agreement with the experimental data. The internal length scale can be used to characterize the scale effect on creep for rockfill. The creep strain and creep strain rate of bigger size particles are larger than the smaller particles under the same load conditions, which show a good agreement with the test data and engineering observation data.The proposed model can provide guidance for using test parameters to predicte the creep behaviors in engineering.