High Earth-rockfill Dams Research Articles

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...

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.

Nonlinear finite element analysis of effect of seismic waves on dynamic response of Shiziping dam

Many high earth-rockfill dams are constructed in the west of China. The seismic intensity at the dam site is usually very high, thus it is of great importance to ensure the safety of the dam in meizoseismal area. A 3D FEM model is established to analyze the seismic responses of Shiziping earth-rockfill dam. The nonlinear elastic Duncan-Chang constitutive model and the equivalent viscoelastic constitutive model are used to simulate the static and dynamic stress-strain relationships of the dam materials, respectively. Four groups of seismic waves are inputted from the top of the bedrock to analyze the dynamic responses of the dam. The numerical results show that the calculated dynamic magnification factors display a good consistency with the specification values. The site spectrum results in larger acceleration response than the specification spectrum. The analysis of relative dynamic displacement indicates that the displacement at the downstream side of the dam is larger than that at the upstream side. The displacement response reduces from the center of river valley to two banks. The displacement responses corresponding to the specification spectrum are a little smaller than those corresponding to the site spectrum. The analysis of shear stress indicates that a large shear stress area appears in the upstream overburden layer, where the shear stress caused by site waves is larger than that caused by specification waves. The analysis of dynamic principal stress indicates that the minimum dynamic stresses in corridor caused by specification and site waves have little difference. The maximum and minimum dynamic stresses are relatively large at two sides. The largest tensile stress occurs at two sides of the floor of grouting corridor, which may result in the crack near the corridor side. The numerical results present good consistency with the observation data of the grouting corridor in Wenchuan earthquake.

Comparison between Duncan and Chang’s EB Model and the Generalized Plasticity Model in the Analysis of a High Earth-Rockfill Dam

Nonlinear elastic model and elastoplastic model are two main kinds of constitutive models of soil, which are widely used in the numerical analyses of soil structure. In this study, Duncan and Chang's EB model and the generalized plasticity model proposed by Pastor, Zienkiewicz, and Chan was discussed and applied to describe the stress-strain relationship of rockfill materials. The two models were validated using the results of triaxial shear tests under different confining pressures. The comparisons between the fittings of models and test data showed that the modified generalized plasticity model is capable of simulating the mechanical behaviours of rockfill materials. The modified generalized plasticity model was implemented into a finite element code to carry out static analyses of a high earth-rockfill dam in China. Nonlinear elastic analyses were also performed with Duncan and Chang's EB model in the same program framework. The comparisons of FEM results andin situmonitoring data showed that the modified PZ-III model can give a better description of deformation of the earth-rockfill dam than Duncan and Chang’s EB model.

Numerical analysis of the anti-seepage measures for high earth rockfill dam on deep overburden

The anti-seepage measures of a high earth rockfill dam built on the foundation with a deep overburden affects the stability and safety of the dam greatly. Nowadays there are few researches on this area both at home and abroad. On the basis of the finite element seepage analysis of the Pubugou high rockfill dam in which core walls and two cut-off walls are designed as the anti-seepage measures, the real seepage behavior of the seepage field is obtained in this paper, as well as the seepage characters of the seepage field under different arrangements of the cut-off walls. The conclusions have a certain referential value for the design of the anti-seepage measures for the similar projects with the foundation of a deep overburden.

Study of Mechanical Properties of Soil-Cement Mixture for a Cutoff Wall

A series of triaxial compression tests on soil-cement mixture samples has been made in order to investigate its mechanical properties. The test results show that as the confining pressure increases, the strength and the strain at peak stress of this soil-cement mixture increase drastically and the initial modulus changes very little. The failure mode is a plastic-shearing one imposed by the confining pressure. These results are different from the previous ones for a soil-cement mixture being brittle and of low strength obtained based on unconfined compression tests, where the condition does not satisfy the actual in situ stress condition for the cutoff wall. The study suggested an important idea of using a soil-cement mixture instead of common concrete to construct a deep cutoff wall under high earth-rockfill dams. This has been proved by the stress-displacement analysis by FEM for a high earth-rockfill dam with a cutoff wall in deep alluvium.

Joint spatial behavior of a high earth-rockfill dam and its upstream cofferdam with consideration of the time factor

1. A increase of the height of the dam by stages as well as in construction time has a considerable effect on the SSS of the cofferdam, especially from stage II to VI. 2. Development of stages of construction of the dam and its construction time leads to the following changes in the SSS of the cofferdam: The levels of normal stressesσx,σy increase on average by more than 2 times; the level of the safety factors decrease by about 2 times, the minimum stabilized value Ksa=1.5; vertical movements increase, the maximum values reach 0.68 m in the middle of the downstream slope of the cofferdam, and the settlement of the crest bench marks is 0.4 m, horizontal movements change but insignificantly. 3. The rate of variation of the SSS is different for different points of the cofferdam body, decreasing on approaching the upstream slope. 4. After the VI stage of constructing the dam, the SSS of the cofferdam changes little, i.e., the SSS stabilizes. The causes of stabilization are: The effect of the dam design, i.e., the height of the dam and distance of the layer being built-up to the cofferdam; effect of three-dimensionality of the site, i.e., the overlying part of the dam is retained on the canyon walls and cannot transfer its weight to the lower part; the dam is constructed over the course of many years, and therefore creep subsequently after the end of construction develops very slowly with time and its amount is small. 5. For high earth-rockfill dams being constructed in a narrow site, the SSS of the lower part of the dam changes little, when the dam is brought to more than half the height, the load is transferred by friction to the canyon walls.