Earth-rockfill Dam Research Articles

Dam Safety Analysis Based on Stepwise Regression Model

The simulating and predicting analysis model is studied by the deformation monitoring data of Bikou earth-rockfill dam. Based on the least squares method of Statistics principles, the stepwise regression model has been established of earth-rockfill dam deformation displacement, which is used to fit and forecast the measured deformation data sequences of dam. The results shows that the deformation monitoring model of Bikou earth-rockfill dam having higher fitting precision, longer predict cycle, can be better applied to the fitting and prediction of dam deformation monitoring data.

Comparison between the Isotope Tracking Method and Resistivity Tomography of Earth Rock-Fill Dam Seepage Detection

This paper compares the different inversion results of three different earth rock-fill dam models with the actual leakage passages by performing isotope tracing tests and resistivity tomographic tests. The accuracy of the experimental results is evaluated, and the characteristics of these two methods are analyzed. As a result, some significant references are offered for earth rock-fill dam’s hidden defects detection. The experimental results show that the leakage and the direction of the seepage can be judged by isotope tracing tests, meanwhile, the degree of the leakage can be confirmed through the determination of the horizontal seepage velocity and the vertical seepage velocity, but it is difficult to properly determine the position of leakage passages and the range of leakage. Relatively speaking, the positions of the leakage passages can be accurately and directly displayed through resistivity tomographic tests. The experiment results show that the resistivity tomographic method is much better than isotope tracing method with regard to earth rock-fill dam’s hidden defects detection, and the resistivity tomographic method expresses much more convenience and much higher precision than isotope tracing method.

Nonlinear elastic model for compacted clay concrete interface

In this paper, a nonlinear elastic model was developed to simulate the behavior of compacted clay concrete interface (CCCI) based on the principle of transition mechanism failure (TMF). A number of simple shear tests were conducted on CCCI to demonstrate different failure mechanisms; i.e., sliding failure and deformation failure. The clay soil used in the test was collected from the “Shuang Jang Kou” earth rockfill dam project. It was found that the behavior of the interface depends on the critical water contents by which two failure mechanisms can be recognized. Mathematical relations were proposed between the shear at failure and water content in addition to the transition mechanism indicator. The mathematical relations were then incorporated into the interface model. The performance of the model is verified with the experimental results. The verification shows that the proposed model is capable of predicting the interface shear stress versus the total shear displacement very well.

Experimental study on fracture toughness and tensile strength of a clay

Fracture toughness K IC is an important mechanical parameter of a material to indicate its ability to resist fracture failure under mode I load conditions in fracture mechanics. The method to determine K IC of geomaterials and the relationship between K IC and other mechanical parameters such as tensile strength σ t were paid close attention by many studies. In this study, the K IC of a clay, which is the core material of a high earth-rock fill dam in Western China, was determined by an improved 3-point bending beam loading assembly on single edge cracked soil beams. The testing results indicated that linear elastic fracture mechanics is suitable for investigating the fracture behavior of the clay. The values of the K IC of the clay vary from 7.10 to 31.43 kPam 0.5 with changing water contents or dry densities of the soil beams. The σ t of the clay was investigated by a uniaxial tension loading assembly on cylindrical compacted specimens. The testing results indicated that the tensile failure of the soil columns is brittle, and the strain before failure can be neglected. The values of the σ t of the clay vary from 19.00 to 90.00 kPa with changing water contents or dry densities of the soil columns. Based on testing data, an empirical linear relationship between the K IC and the σ t of the tested clay, which is K IC = 0.3546 σ t, was suggested. By analyzing other studies, it was found that the fracture toughness and tensile strength of many geomaterials such as cohesive soil, frozen soil, soft rock and hard rock are also linearly correlated. But the proportionality coefficients are different for different soils or rocks and testing methods.

Hydraulic fracturing of rock-fill dam

The condition in which hydraulic fracturing in core of earth-rock fill dam maybe induced, the mechanism by which the reason of hydraulic fracturing canbe explained, and the failure criterion by which the occurrence of hydraulicfracturing can be determined, were investigated. The condition dependson material properties such as, cracks in the core and low permeability ofcore soil, and “water wedging” action in cracks. An unsaturated core soiland fast impounding are the prerequisites for the formation of “waterwedging” action. The mechanism of hydraulic fracturing can be explainedby fracture mechanics. The crack propagation induced by water pressuremay follow any of mode I, mode II and mixed mode I-II. Based on testingresults of a core soil, a new criterion for hydraulic fracturing was suggested,from which mechanisms of hydraulic fracturing in the core of rock-fill damwere discussed. The results indicated that factors such as angle betweencrack surface and direction of principal stress, local stress state at thecrack, and fracture toughness KIC of core soil may largely affect theinduction of hydraulic fracturing and the mode of the propagation of thecrack.The condition in which hydraulic fracturing in core of earth-rock fill dam maybe induced, the mechanism by which the reason of hydraulic fracturing canbe explained, and the failure criterion by which the occurrence of hydraulicfracturing can be determined, were investigated. The condition dependson material properties such as, cracks in the core and low permeability ofcore soil, and “water wedging” action in cracks. An unsaturated core soiland fast impounding are the prerequisites for the formation of “waterwedging” action. The mechanism of hydraulic fracturing can be explainedby fracture mechanics. The crack propagation induced by water pressuremay follow any of mode I, mode II and mixed mode I-II. Based on testingresults of a core soil, a new criterion for hydraulic fracturing was suggested,from which mechanisms of hydraulic fracturing in the core of rock-fill damwere discussed. The results indicated that factors such as angle betweencrack surface and direction of principal stress, local stress state at thecrack, and fracture toughness KIC of core soil may largely affect theinduction of hydraulic fracturing and the mode of the propagation of thecrack.

An intelligent displacement back-analysis method for earth-rockfill dams

An intelligent method for the effective displacement back-analysis of earth-rockfill dams was proposed by combining artificial neural networks and evolutionary calculation. This method employs artificial neural networks, with optimal architecture trained by the evolutionary calculation and Vogl’s algorithm, instead of the time-consuming finite element analysis. In the back analysis, the soil parameters were optimized by performing evolutionary calculations on the tested neural network. The proposed method was verified by applying it to the displacement back-analysis of two projects in China, and the influence of generation number and set size on the simulation ability of neural networks was investigated.

Stability of earth–rockfill dams: Influence of geometry on the three-dimensional effect

A series of parametric studies were performed to investigate the three-dimensional (3D) effect on the stability of an earth–rockfill dam, with respect to some major factors, such as geometrical characteristics of the dam and topography of the canyon. The length–height ratio of the earth–rockfill dam clearly influences the 3D safety factor. A power function suitably expresses the relationship between the increment ratio for the safety factor and the length–height ratio. The canyon shape, gradient of dam slope and height of the dam significantly influence the 3D effect. The results may be used as a blueprint by combining the two-dimensional (2D) safety factor in common use, and the relationship between 2D and 3D safety factors established in this study.

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.

Design, construction control, and performance of the Svartevann earth-rockfill dam : Kjaernsli, B; Kvale, G; Lunde, J; Baade-Mathiesen, J Norw Geotech Inst PublN142, 1982, 8P

Design, construction control, and performance of the Svartevann earth-rockfill dam : Kjaernsli, B; Kvale, G; Lunde, J; Baade-Mathiesen, J Norw Geotech Inst PublN142, 1982, 8P

Performance of earth and earth-supported structures : CONFERENCE Vol. 1 Part 2. Proc. Speciality conference, Purdue Univ. June 1972. Figs, Tabls, Refs. ASCE, NEW YORK, V1, PART 2, 1972, 670P

Proceedings of the Specialty Conference on Performance of Earth and Earth-Supported Structures held at Purdue University, Lafayette, Indiana, June 11-14, 1972. Sponsored by the School of Civil Engineering at Purdue University and the Soil Mechanics and Foundations Division of ASCE. Performance of Earth and Earth-Supported Structures contains dozens of papers covering a broad range of relevant issues in earthen structure performance. Topics include embankments on soft ground, earth and earth-rockfill dams, shallow foundations, deep foundations, and soil-structure interaction. These proceedings will be of interest to both practitioners and researchers working with earth and earth-supported structures.