Analysis of earth dam failures: A database approach

A dam may fail when the loading exceeds the resistance against overtopping, internal erosion, slope instability, sliding/overturning, excessive deformation etc. To investigate the causes of failures, it is necessary to study characteristics of the dams which have experienced failures. In this work, more than 1600 dam failure cases throughout the world excluding China are compiled into a database, including details of the dams, the reservoirs, the triggers and the failures. This paper focuses on failure of earth dams, which make up 66% of the failure cases in the database. A statistical analysis of the failure characteristics is conducted. According to dam zoning and corewalls, earth dams are divided into four typical categories: homogeneous earthfill dams, zoned earthfill dams, earthfill dams with corewalls, and concrete faced earthfill dams. Further analysis of the failure modes and causes of the four types of earth dams is carried out. Potential locations at risk are also described to provide the reader with a better understanding of earth dam failures.[1]


The Seismic Coefficient in Earth Dam Design

The limitations of methods of earthquake-resistant design of embankments based on pseudo-static analysis and incorporating a static seismic force designated by a seismic coefficient are discussed. It is suggested that both from considerations of soil behavior under cyclic loading conditions, and for purposes of assessing embankment deformations due to earthquakes, the development of a method of predicting dynamic seismic forces and their variations with time would provide a more reasonable approach for design purposes. A method of accomplishing this objective is suggested, and representation of the results by an equivalent simplified seismic force series is proposed. For embankments that can be considered to have a uniform shear modulus, charts are presented for determination of the equivalent seismic force series. It is pointed out that limitations in available dynamic response analyses require that some judgment be exercised in selecting design parameters. However, the results presented in the paper provide a useful basis for guiding this judgment. Furthermore, the results show that in designating seismic coefficients for design purposes, it is important to distinguish between embankments of different heights and material characteristics as well as different positions of the potential slide mass within the embankment.[2]


Analysis of Gradual Earth‐Dam Failure

Analytical models are developed for the simulation of earthdam breach erosion. Using a reservoir water‐mass depletion equation, broad‐crested weir hydraulics and a breach‐erosion relation, solutions are derived for rectangular, triangular, and trapezoidal‐shaped breaches. Breach erosion is assumed to be either a linear or quadratic function of the outflow mean water velocity. Historical data are used to test the models. A sensitivity analysis is performed to determine the importance of the various parameters involved.[3]


Earth-Dam Practice in the United States

This paper presents a brief history of earth and rock-fill clams, including a discussion of the types of failure to which such clams have been subject. General features of projects are covered including outlet conduits, spillways, riprap, and the earth embankment itself. Since, in many instances, adequacy of the appurtenant works determines the safety and economy of a project, these features are discussed. Best current practice in design and construction is described with detailed reference to slope stability, slope protection, cutoff and core walls, earthquakes, costs, maintenance, and grouting. Predictions of future advances are set forth, and helpful design criteria are outlined. An extensive Bibliography adds materially to the over-all value.[4]


Nonlinear Dynamic Analyses of an Earth Dam

The following investigations are presented: (1) Comparison between the results of 2D nonlinear and 3D nonlinear dynamic finite element analyses of an earth dam subject to two very different input ground motions; and (2) comparison between measured and computed earthquake responses of the dam. The study is based on rigorous nonlinear hysteretic analyses utilizing a multi‐surface plasticity theory. The backbone shear stress‐strain curve is assumed hyperbolic and symmetrical about the origin. Detailed comparisons of induced stresses, strains, accelerations, and permanent deformations at various locations in the dam are presented. The effects of three‐dimensionality on the dynamic response, particularly on resulting permanent deformations, are assessed. The suitability of 2D analyses in determining the dynamic behavior of such structures is evaluated.[5]


Reference

[1] Zhang, L.M., Xu, Y. and Jia, J.S., 2009. Analysis of earth dam failures: A database approach. Georisk, 3(3), pp.184-189.

[2] Seed, H.B. and Martin, G.R., 1966. The seismic coefficient in earth dam design. Journal of the Soil Mechanics and Foundations Division, 92(3), pp.25-58.

[3] Singh, V.P. and Scarlatos, P.D., 1988. Analysis of gradual earth-dam failure. Journal of hydraulic engineering, 114(1), pp.21-42.

[4] Middlebrooks, T.A., 1953. Earth-dam practice in the United States. Transactions of the American Society of Civil Engineers, 118(2), pp.697-722.

[5] Prevost, J.H., Abdel-Ghaffar, A.M. and Lacy, S.J., 1985. Nonlinear dynamic analyses of an earth dam. Journal of Geotechnical Engineering, 111(7), pp.882-897.