Time-Dependent Deformations of Rockfill Dams

Mohammad Kermani, Jean-Marie Konrad

In the proceedings of: GeoRegina 2014: 67th Canadian Geotechnical Conference

Session: Infrastructure

ABSTRACT: ndent Deformations of Rockfill Dams Mohammad Kermani and Jean-Marie Konrad Department of civil and water engineering, Université Laval, Québec, QC, Canada ABSTRACT Several studies can be found in the literature in which deformations of different rockfill dams are presented and compared. However, this fact is often neglected that these deformations take place during three main phases in lifetime of a rockfill dam: construction, impoundment and operation. Correspondingly, few concentrated studies are done on the long-term deformations, i.e., during operation period of rockfill dams. In this paper, the factors that influence the time-dependent behavior of rockfill dams are reviewed according to the past studies. The field observations are compared to the results of the experimental works and justified with existing theories about rockfill compression. Finally, a new approach for prediction of the long-term deformations of rockfill dams is introduced. RÉSUMÉ Plusieurs études peuvent être trouvées dans la littérature dans lesquelles les déformations de plusieurs barrages en enrochement sont présentées et comparées. Par contre, le fait que ces déformations ont lieu pendant les trois phases principales de la vie d'un barrage, soit la construction, la mise en eau et la période d'opération, est habituellement négligé. Par conséquence, il y a peu d'études réalisées sur les déformations à long-terme, i.e., pendant la période d'opération du barrage en enrochement. Cet article présente d'abord une revue de littérature sur les paramètres qui influencent le comportement en fonction du temps pour les barrages en enrochement. Ensuite, les observations de terrain sont comparées avec les travaux de laboratoire et avec les théories existantes sur la compression d'enrochement. Finalement, une nouvelle approche visant à prédire les déformations à long-terme des barrages en enrochement est introduite. 1 INTRODUCTION Rockfill is identified by large grains (average size of at least 5 cm and maximum size of up to 2m), great variety of particle sizes, shapes and minerals. As a consequence, a full scale experimental study on rockfill material is almost impossible. Thus, there are severe uncertainties about using concepts of classical soil mechanics to evaluate the strength and deformation behavior of rockfill. Accordingly, the design of rockfill embankments, rockfill dams for instance, has been mostly based on engineering judgments and experiences. However, this is not sufficient, because any project has unique geometry, material properties and boundary conditions that need to be evaluated through relevant tools; i.e., laboratory and field experiments and numerical modeling. In order to implement our knowledge of rockfill behavior in dam engineering, it is important to notice that the total failure and slope stability are not serious concerns in the design of rockfill dam structures. because there are very few clues of total failure of the structure in the literature (Milligan & Coyne, 2005). The dam deformations during and after construction on the other hand, must be analyzed because: It is necessary to decide the height of the dam's camber, The deformations should be taken into consideration when designing construction elements that can resist a certain amount of displacement, It is necessary to arrange a compatible (long-term and short-term) compressibility between different zones to avoid (core) cracking, An early warning system (as proposed by Clements, 1984) can be contrived in the dam which compares predicted and measured settlements or settlement rates in every moment and warns about unusual displacements. There are several studies in the literature in which settlements of different rockfill dams are presented and compared. Almost in all of these studies, the crest horizontal and vertical displacements are considered as the index for comparison. The studies can be categorized into two groups: first, the earlier studies in which an implicit equation is suggested for prediction of deformations in dams. These equations are mainly of three types: logarithmic relationships (strain vs. log time) (Sowers et al., 1965), power type relationships (Soydemir & Kjaernsli, 1979) or strain rate versus time (Parkin, 1977). Second group includes the more recent studies that suggest a qualitative judgment procedure. In these studies, they claim that the settlement behavior of the rockfill dams is more complicated than can be captured by a single empirical equation and is a function of several factors. So, the final deformation of the embankment can be estimated by comparing it to similar cases in terms of the influencing factors. A summary of the previous field studies on the deformation behavior of rockfill dams and the studied influencing factors is presented in Table 1. Because of the restrictions in studying the time effects experimentally, and also the variety of parameters that influence the behavior of rockfill dams in the field, the behavior during the operation stage is still ambiguous. During the operation period, creep deformations,

RÉSUMÉ: -Dependent Deformations of Rockfill Dams Mohammad Kermani and Jean-Marie Konrad Department of civil and water engineering, Université Laval, Québec, QC, Canada ABSTRACT Several studies can be found in the literature in which deformations of different rockfill dams are presented and compared. However, this fact is often neglected that these deformations take place during three main phases in lifetime of a rockfill dam: construction, impoundment and operation. Correspondingly, few concentrated studies are done on the long-term deformations, i.e., during operation period of rockfill dams. In this paper, the factors that influence the time-dependent behavior of rockfill dams are reviewed according to the past studies. The field observations are compared to the results of the experimental works and justified with existing theories about rockfill compression. Finally, a new approach for prediction of the long-term deformations of rockfill dams is introduced. RÉSUMÉ Plusieurs études peuvent être trouvées dans la littérature dans lesquelles les déformations de plusieurs barrages en enrochement sont présentées et comparées. Par contre, le fait que ces déformations ont lieu pendant les trois phases principales de la vie d'un barrage, soit la construction, la mise en eau et la période d'opération, est habituellement négligé. Par conséquence, il y a peu d'études réalisées sur les déformations à long-terme, i.e., pendant la période d'opération du barrage en enrochement. Cet article présente d'abord une revue de littérature sur les paramètres qui influencent le comportement en fonction du temps pour les barrages en enrochement. Ensuite, les observations de

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Cite this article:
Mohammad Kermani; Jean-Marie Konrad (2014) Time-Dependent Deformations of Rockfill Dams in GEO2014. Ottawa, Ontario: Canadian Geotechnical Society.

@article{GeoRegina14Paper250,author = Mohammad Kermani; Jean-Marie Konrad,title = Time-Dependent Deformations of Rockfill Dams,year = 2014}