Bingyin Zhang

Displacement-Based Back-Analysis of the Model Parameters of the Nuozhadu High Earth-Rockfill Dam

The parameters of the constitutive model, the creep model, and the wetting model of materials of the Nuozhadu high earth-rockfill dam were back-analyzed together based on field monitoring displacement data by employing an intelligent back-analysis method. In this method, an artificial neural network is used as a substitute for time-consuming finite element analysis, and an evolutionary algorithm is applied for both network training and parameter optimization. To avoid simultaneous back-analysis of many parameters, the model parameters of the three main dam materials are decoupled and back-analyzed separately in a particular order. Displacement back-analyses were performed at different stages of the construction period, with and without considering the creep and wetting deformations. Good agreement between the numerical results and the monitoring data was obtained for most observation points, which implies that the back-analysis method and decoupling method are effective for solving complex problems with multiple models and parameters. The comparison of calculation results based on different sets of back-analyzed model parameters indicates the necessity of taking the effects of creep and wetting into consideration in the numerical analyses of high earth-rockfill dams. With the resulting model parameters, the stress and deformation distributions at completion are predicted and analyzed.

Influence of Shear on Permeability of Clayey Soil

AbstractThe variation of stress–strain state induces changes in the permeability of clayey soil and then affects the properties of seepage and consolidation. In previous studies, variations of the permeability of soil in shear process were mainly neglected, and there were no reasonable descriptions of the permeability in such a condition. To study the variation of the hydraulic conductivity of clayey soil in shear process, new triaxial seepage equipment was designed by changing the conventional triaxial apparatus. Based on a series of tests under different confining pressures carried out by this equipment, the influences of the stress–strain state of clayey soil on hydraulic conductivity were investigated. Furthermore, a mathematical model for the hydraulic conductivity of clayey soil under the condition of large shear deformation was proposed. The comparison between the seepage test results and the calculated values of the proposed model indicates that the mathematical model can calibrate the effects of ...

Consolidation Analysis of Nuozhadu High Earth-Rockfill Dam Based on the Coupling of Seepage and Stress-Deformation Physical State

AbstractA consolidation analysis method for an earth-rockfill dam based on the coupling of physical state, stress deformation, and seepage was established. In this method, a permeability coefficient model considering physical state and shear stress level was introduced, and it was integrated with Biot’s consolidation theory to simulate the coupling relationship. Taking the Nuozhadu high earth-rockfill dam as an example, a parameter back-analysis method using a neural network and evolutionary algorithm was applied to back-analyze the permeability coefficient model parameters of the core material based on observation data of pore water pressure in the dam. Then, consolidation numerical analyses were performed by using the back-analyzed parameters and the constant permeability measured in situ, respectively. The spatial and temporal distribution of pore water pressure calculated by the back-analyzed parameters coincided quite well with the monitoring data during construction and operation. However, the numer...

Particle Breakage of Cement Ellipsoid Aggregate—Part I: Triaxial Compression Tests

Cement ellipsoid aggregate was adopted to simulate rockfill materials in laboratory tests. The specimen was prepared by mixing cement ellipsoids of four diameters in a particular ratio. Triaxial compression tests and isotropic compression tests were then conducted to investigate the macroscopic stress–strain relationship of the aggregate, and the crushing characteristics of the cement ellipsoids. The particle size distributions were analyzed after testing. No particle breakage occurred during the isotropic compression tests or the unloading–reloading process of the triaxial compression tests; this implied that breakage of the cement ellipsoids mainly occurs during the shearing process of loading. Sieving analysis showed that the sizes of the larger particles did not change much; crushing mainly produced small particles and, thus, changed the particle size distribution.