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A curious phenomenon of significant summertime downslope movements, observed at other sites where trees grow on the lower slope of clay fill embankments, has been recorded during 10 years of downstream slope monitoring at Aldenham embankment dam, UK. The data from four monitored sections of the slope are described. At two locations, downslope movements were observed in high soil moisture deficit (SMD) conditions, where it appeared that high SMD and shrinkage caused by trees growing on the lower slope allowed the grassed upper slope with lower SMD to slip downwards under its own weight. This led to a seasonal, ratcheting accumulation of crest settlement - a type of mechanism that presents a continual serviceability problem to infrastructure embankments as well as dams. This mechanism was simulated in a qualitative way by finite difference analysis. At a third monitored section, a sparser distribution of lower water-demand trees, lower plasticity clay fill, and a moisture content close to or below the plastic limit appeared to result in insignificant slope movements. At a fourth low-height monitored section, a slow accumulation of downslope movements, as well as tension cracking, was observed. [ABSTRACT FROM AUTHOR]

This paper describes a series of laboratory tests performed to characterize the mechanical and hydraulic properties of plastic concrete (PL-C). PL-C is used in the construction of seepage cut-off walls in dams and it comprises cement, aggregate, and water mixed with sodium bentonite. The addition of sodium bentonite causes a reduction in strength and improved ductility after failure compared with normal concrete. The mechanical properties of PL-C are studied using a series of unconfined compression tests and confined compression tests performed while simultaneously permeating water through PL-C specimens. Stress relaxation and controlled rate of loading tests are also performed to investigate the rate-sensitivity and time-dependency of plastic concrete. The test results show that the hydraulic conductivity of PL-C increases between two and three orders of magnitude during triaxial compression due to yielding, crack formation, and dilation of the cracks. Such changes in the behaviour of PL-C should be minimized during design by controlling the working strains and using erosion-resistant mixes. In addition to these findings, PL-C exhibits significant time-dependent behaviour similar to that observed for clays, and the variation of compressive strength versus confining stress is comparable to normal strength concrete. Cet article décrit une série d’essais en laboratoire effectués dans le but de caractériser les propriétés mécaniques et hydrauliques du béton plastique (BP). Le BP est utilisé dans la construction de systèmes de coupure dans les barrages. Il est constitué du ciment, de l’agrégat et de l’eau mélangé avec de la bentonite de sodium. L’ajout de bentonite de sodium entraîne une réduction de la résistance et une amélioration de la ductilité suite à la rupture, comparativement au béton standard. Les propriétés mécaniques du BP sont étudiées à l’aide d’essais en compression non confinés et confinés effectués en même temps que l’eau pénètre à travers les échantillons de BP. Des essais de relaxation des contraintes et de chargement à taux contrôlé ont aussi été effectués pour investiguer la sensibilité au taux et la dépendance au temps des BP. Les résultats des essais montrent que la conductivité hydraulique du béton plastique augmente de deux à trois ordres de grandeur durant la compression triaxiale en raison de l’écoulement, de la formation de fissures et de la dilatation dans les fissures. Ces changements dans le comportement du BP devraient être minimisés durant la conception par un contrôle des déformations et par l’utilisation de mélanges résistants à l’érosion. De plus, le béton plastique démontre un comportement dépendant du temps de façon significative, comme ce qui est observé pour les argiles, et la variation de la contrainte compressive versus la contrainte de confinement est comparable à la résistance normale d’un béton. [ABSTRACT FROM AUTHOR]

Post-earthquake inspection is required by many dam safety regulations. Typically, based on the magnitude of the earthquake, the guidelines define an area within which dams should be inspected. The areas are established on ground-motion relations derived for the western United States. In eastern North America (ENA), the attenuation is slower with distance from the earthquake epicentre, and as a consequence the inspection area should be significantly larger than that recommended by the current guidelines. We review the state of knowledge on earthquake damage to dams, the factors used to define post-earthquake inspections, and the earthquake characteristics used to define the guidelines. We recommend new radii of inspections for dams applicable in ENA, including the Province of Quebec. Derived from historical earthquake information, the proposed new radii of inspections are twofold to sixfold larger than the 1988 guidelines of the International Commission on Large Dams. It is also suggested that a half-magnitude unit be added to every magnitude “rapidly” released by seismological organizations to include the intrinsic uncertainty in magnitude values and types. Our proposed approach is only one avenue that dam owners can follow to comply with dam safety regulations. Irrespective of the avenue chosen, however, this paper emphasizes the need for dam owners to consider the lower ground motion attenuation in ENA. [ABSTRACT FROM AUTHOR]

Quantitative investigations, including two aquifer tests and development of a three-dimensional (3D) groundwater flow model, were required to determine the hydraulic connection between an irrigation reservoir and a buried valley aquifer in southern Alberta. Evidence of seepage was detected in the buried valley aquifer 10 km east of the Pine Coulee reservoir at the onset of filling in 1999, when the reservoir level exceeded an elevation of 1035 m above sea level (a.s.l.). Concern for an increase in the local water table and the creation of artesian conditions in the aquifer prompted this study to determine the approximate location of a seepage window that appeared to be connecting the reservoir and aquifer. Observations of hydraulic head in the aquifer during the pumping tests revealed a barrier boundary when the reservoir level was at an elevation of 1035 m a.s.l. and a recharge boundary condition when the elevation exceeded 1039 m a.s.l. These data were used to calibrate a 3D groundwater flow model, which was needed to determine the hydraulic properties and approximate location of the leakage zone. The quantitative investigation showed that seepage likely occurred through the sideslopes of the flooded coulee, rather than through the low-permeability coulee floor sediments or the embankment dam. Further simulations illustrated the expected seepage rates at various reservoir supply levels and the pumping rates required for relief wells installed in the buried valley aquifer to maintain historic aquifer hydraulic head. A brief postanalysis indicated that the forecasted pumping rates were only 15% lower than have been required to maintain preconstruction water levels in the buried valley aquifer. [ABSTRACT FROM AUTHOR]

The analysis of stress–strain behaviour and the effects of submergence on quarried rock shells, used mainly in dams but also in road construction, is of major importance from both economic and safety points of view. The research work presented here starts with an in-depth review of the nonlinear elastic procedure widely used in rockfill analyses since 1970, its later application to simulate wetting effects, and the latest published modifications to the so-called hyperbolic stress–strain model. An update of the existing wetting simulation procedure has been formulated, calculation routines to analyze constructional behaviour and wetting effects on rockfills have been implemented, and the methodology developed has been applied to a structure 100 m high. Calculation routines have been written to run in FLAC, a finite difference based code that incorporates a programming language. The analyzed structure is part of a road rockfill located at the Contreras Reservoir in Spain and consists specifically of two shell-shaped cross sections subjected to the influence of submergence. The results are expected to be useful in estimating collapse settlements in the upstream shells of earth-core dams. [ABSTRACT FROM AUTHOR]

The paper proposes equations describing the transport of gases through the initially unsaturated core of a dam by dissolution and diffusion in water and examines different numerical simulations based on these equations. The simulation results provide pore-water pressure distributions similar to those observed in several earth dams, with higher pore-water pressures than expected in the downstream part of the core. Practical considerations to estimate the implications of the phenomenon are then discussed.Key words: dam, unsaturated soil, pore pressure, dissolution of gas, diffusion of gas, hydraulic conductivity.L'article propose des équations décrivant le transport des gaz par dissolution et diffusion dans l'eau à travers le noyau initialement non saturé d'un barrage et examine différentes simulations numériques basées sur ces équations. Les résultats des simulations fournissent des distributions de pressions interstitielles semblables à celles observées dans plusieurs barrages en terre, avec des pressions interstitielles plus élevées qu'escomptées dans la partie aval du noyau. On discute alors de considérations pratiques pour évaluer les implications du phénomène.Mots clés : barrages, sol non saturé, pression interstitielle, dissolution des gaz, diffusion des gaz, conductivité hydraulique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

The seepage rate through homogeneous or zoned dikes includes saturated and unsaturated flow. The latter is often neglected but should be considered to obtain the positions of the water table and the seepage face that may develop either on the downstream slope of a homogeneous dike or within the filter layer behind the core of a zoned dike. Different dikes with heights of 5, 10, 20, and 50 m have been analyzed numerically with a two-dimensional finite element code. The cases investigated include the most frequent types of small dikes designed to retain municipal or industrial wastewater. Solutions are proposed to solve numerically two difficulties related to the representation of saturated and unsaturated physical flow conditions. One difficulty is treating a downstream seepage face. The other is treating the passage of water from the core into a draining layer. The paper presents simple expressions to predict the total (saturated and unsaturated) seepage flow rate through a dike and discusses precautions to be taken.Key words: dams, dikes, seepage, saturated soil, unsaturated soil, numerical modeling.Le débit de fuite des digues homogènes ou zonées inclut les écoulements saturés et non saturés. Ces derniers sont souvent négligés mais devraient être considérés pour avoir les positions de la nappe et de la surface de suintement qui peut se développer sur la pente aval d'une digue homogène ou dans le filtre à l'arrière du noyau d'une digue zonée. Différentes digues de hauteurs 5, 10, 20 et 50 m ont été analysées numériquement avec un code bidimensionnel d'éléments finis. Les cas étudiés comprennent les types les plus fréquents de petites digues conçues pour retenir des eaux usées municipales ou industrielles. On propose des solutions pour résoudre numériquement deux difficultés reliées à la représentation des conditions physiques d'écoulement saturé et non saturé. Une difficulté est le traitement d'une surface de suintement. L'autre est le traitement du passage de l'eau du noyau dans une couche drainante. L'article propose des expressions simples pour prédire le débit de fuite total (saturé et non saturé) à travers une digue et discute des précautions à prendre.Mots clés : barrages, digues, écoulement, sol saturé, sol non saturé, modèle numérique. [ABSTRACT FROM AUTHOR]