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«Experimental study of breach mechanics in overtopped noncohesive earthen embankments Mahmoud Al-Riffai Thesis submitted to the Faculty of Graduate ...»

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Experimental study of breach mechanics in overtopped

noncohesive earthen embankments

Mahmoud Al-Riffai

Thesis submitted to the

Faculty of Graduate and Postdoctoral Studies

In partial fulfillment of the requirements for the degree of

Doctorate of Philosophy in Civil Engineering (Water Resources)

Under the auspices of the Ottawa-Carleton Institute of Civil Engineering (OCICE)

Department of Civil Engineering

Faculty of Engineering

University of Ottawa

© Mahmoud Al-Riffai, Ottawa, Canada, 2014 Ioan Nistor (University of Ottawa)

DIRECTEUR (DIRECTRICE) DE LA THÈSE / THESIS SUPERVISOR

EXAMINATEURS (EXAMINATRICES) DE LA THÈSE / THESIS EXAMINERS

Ana Maria A.F. da Silva (Queen’s University) Paul J. Van Geel (Carleton University) Colin D. Rennie (University of Ottawa) Sai K. Vanapalli (University of Ottawa) Thursday, July 17, 2014

DATE DE LA SOUTENANCE / DATE OF ORAL DEFENCE

Thesis Committee following defence, 17th July 2014. From left to right: Prof. Paul Van Geel, Dr. Ioan Nistor, Mahmoud Al-Riffai, Prof.

Sai K. Vanapalli, Prof. Ana Maria da Silva, Prof. Colin D. Rennie (Absent: Dr. Eric Lanteigne, Committee Chair) (photo courtesy of Amanj Jamal) Abstract A comprehensive experimental program dealing with three-dimensional overtopping and breach development as well as two-dimensional overtopping physical tests of noncohesive earth embankments has been conducted on scale models in the Hydraulic Laboratory at the Department of Civil Engineering at the University of Ottawa. The experimental program which consisted of three phases focused on geotechnical and hydraulic aspects of the embankment breach mechanism. The first two phases focused on two test series for the three-dimensional breach overtopping tests: drainage and compaction. The test series were designed to determine the embankment breach characteristics using test parameters which have not been adequately identified or controlled in past noncohesive physical models: initial soilwater state and optimum dry unit weight. Both parameters were controlled in laboratory tests by means of compaction effort and seepage through the embankment body, respectively. The dynamic compaction technique employed in the preliminary experimental phase was refined to represent a more realistic method. A novel method was thus designed to simulate the construction of a realsize prototype embankment, where a vibratory and static load was used to apply and control, respectively, the compaction effort. The hydraulic aspects of the embankment breach mechanism were also investigated. For the first time, scale series tests have been used to assess the Froude criterion using tilted and quasiexact geometric scales under very low inflow within the scope of three-dimensional breach overtopping. Data measurements included a time-history of water surface levels and video footage captured from three locations: upstream, downstream and above the embankment models. The analysis for the spatial breach overtopping tests involved measurement of the breach outflow hydrograph and breach channel evolution at the upstream slope, using hydrologic routing and a developed photogrammetric technique using the video footage, respectively. An expression i which estimates the breach outflow based on this apparent upstream control section was therefore derived. The relationship between the measured and estimated breach outflow was expressed in terms of breach discharge efficiency.

The third phase of the experimental program was comprised of two-dimensional overtopping tests to investigate the erodibility of a steep slope in overtopped noncohesive embankment models. A novel experimental two-dimensional configuration used to measure the pore-water-pressures within the embankment model body was developed using micro and standard tensiometer-transducer-probe assemblies, designed, assembled and tested at the Geotechnical Engineering Laboratory. A transient flownet analysis was developed using ArcGIS and the timehistory of the pore-water-pressure measurements. All flow parameters were computed using the free water surface and bed profiles captured using a photogrammetric technique and the developed hydrologic routing method. Using the one-dimensional Saint-Venant equations, an analytical expression for the bed shear stress was derived to take into account the effects of unsteady flow, boundary seepage and steep slopes. Using the measured erosion rates and the sediment continuity principle, the bed mobility relationship expressed by the Shields and transport parameters was revisited to account for the effects of unsteady and supercritical flow on a downstream steep slope in the presence of boundary seepage. This novel transient flownet approach will lead to the development of new sediment mobility relationships for breach flows, instead of the classical sediment transport-capacity formulations which are based on steady, subcritical and normal flow conditions.

iiRésumé

Un programme expérimental intensif traitant le débordement et l’évolution de la brèche en trois dimensions, ainsi que le débordement en deux dimensions d’un ouvrage hydraulique en remblai (barrage ou digue) a été mené. Ces tests physiques ont été effectués sur des modèles réduits de remblais en matériaux non cohésifs dans le laboratoire hydraulique du Département de génie civil de l'Université d'Ottawa. Le programme expérimental comprennait trois phases axé sur les aspects géotechniques et hydrauliques et leur impact sur le mécanisme de la brèche. Les deux premières phases ont porté sur deux séries de tests pour le débordement en trois dimensions: le drainage et le compactage. La série de tests a été conçue pour déterminer les caractéristiques de la brèche digue en utilisant des paramètres de tests qui n’ont pas été identifiés ou mal contrôlés dans des modèles physiques antécédents sur des matériaux non cohésifs: le poids sec unitaire optimal et l’état hydrique initial du sol. Ces deux paramètres ont été contrôlés en laboratoire au moyen de l'effort de compression et un système de drainage du remblai, respectivement. La technique de compactage dynamique employée dans la phase expérimentale préliminaire a été faite de manière améliorée afin d’utiliser une méthode plus réaliste. Cette nouvelle méthode a été conçue pour simuler la construction d'un prototype réel de remblai, où une charge en vibration et une charge statique a été utilisées pour appliquer et contrôler, respectivement, les efforts de compactage. Les aspects hydrauliques du mécanisme d’évolution de la brèche du remblai ont également été étudiés. C’est la première fois que des tests sur un série d’échelles dans de tests de débordement en trois dimensions ont été utilisées pour évaluer le critère de Froude à l'aide d'échelles géométriques inclinés et quasiexactes sous très faible apport. Les données mesurées incluent un historique temporel des niveaux de surface d'eau et des vidéos enregistrées à partir de trois endroits: en amont, en aval et au-dessus du remblai. L'analyse des tests tridimensionnels du débordement comprend les mesures de l'hydrogramme du débit iii de sortie de la brèche et l’évolution du canal de la brèche formé du côté en amont en utilisant la méthode de «laminage hydrologique» et une technique photogramétrique avec des vidéos enregistrées, respectivement. Une expression qui estime le débit de sortie de la brèche sur la section apparente est ainsi obtenue.





La relation entre les mesures et les estimations du débit de sortie de la brèche est considérée comme un paramètre d'efficacité du débit de la brèche.

La troisième phase du programme expérimental est composée de tests en deux dimensions du débordement pour étudier l'érosion de la descente raide dans les modèles de remblai non cohésifs sujet du débordement. Une nouvelle configuration expérimentale en deux dimensions utilisée pour mesurer la pression interstitielles à l'intérieur du remblai du modèle a été développée en utilisant des tensiomètres électroniques très petite taille et d’autres de taille conventionnelle, conçus, assemblés et testés au laboratoire géotechnique. Une analyse de réseau d’écoulement transitoire a été développée en utilisant ArcGIS et les mesures de l’évolution temporelle de la pression interstitielle. Tous les paramètres du débit ont été calculés en utilisant la surface libre de l’eau et les profils du fond à l'aide d'une technique de photogrammétrie et la méthode de laminage hydrologique développé.

En utilisant les équations unidimensionnelles de Saint-Venant, une expression analytique de la contrainte de cisaillement du fond a été introduite pour prendre en compte les effets de l'écoulement instable, les infiltrations aux limites et les descentes raides du remblai. En utilisant les mesures d'érosion et le principe de la continuité des sédiments, la relation de la mobilité du fond exprimée par la formule Shields et le paramètre de transport a été revue pour tenir compte des effets de l'écoulement instable et supercritique sur une descente raide en présence d'une infiltration aux limites. Cette nouvelle approche conduit à l'établissement de nouvelles relations de transport des sédiments pour les débits de la brèche, à la place des formules classiques de transport des sédiments qui sont basés sur des conditions de débit stationnaire constant, conditions d'écoulement sous-critiques et normales.

ivAcknowledgements

I would like to express my sincere and profound gratitude to my thesis supervisor, Dr. Ioan Nistor, for supporting and guiding me throughout this journey that I have embarked over the past few years. Indeed he has gone beyond his duty as a thesis supervisor as he has also assumed the role of both a mentor and a friend during my academic career. His patience and invaluable moral support as well as his belief in my capabilities of both a researcher and teacher, has earned me great professional achievements. He has never failed to endorse me in such prospects and I shall never forget this support.

I am also grateful to Professor Sai Vanapalli for his continuous encouragement and endorsement throughout my academic career, as well as bestowing me his knowledge in the field of classical and unsaturated soil mechanics. I would also like to thank Professor Colin Rennie, Dr. Won Taek Oh and Dr. Jules-Angel InfanteSedano for their advice and discussion on some of the experimental aspects of this this research. Many thanks are directed to Professor Paul Van Geel, from Carleton University, a member of my PhD advisory committee for his valuable comments on the progress and contribution of this thesis. Certainly, the above mentioned, as well as many other professors at the Faculty of Engineering as a whole, have been an inspiration to both my research and teaching experience at the University of Ottawa.

I would also like to express my sincere appreciation to the following technical staff at the University of Ottawa for providing me with expert advice and extraordinary assistance in the acquisition as well as development of the equipment and tools necessary to conduct this research, and from whom I have learnt a vast and

instrumental knowledge:

 Mark Lapointe, Technical Officer of the Hydraulics Laboratory;

v  Jean-Claude Celestin, current Technical Officer and Kulan Ambalavanar, former Technical Officer of the Geotechnical Engineering Laboratory;

 Muslim Majid, Technical Officer of the Structural Engineering Laboratory;

 Leo Denner, Stanley Weedmark, John Perrins, Michael Burns and James Macdermid at the Mechanical and Civil Engineering Machine Shop;

 Dominic Blouin and Xavier Erdmer at the Multimedia Distribution Service It is without doubt that my physical resilience has been challenged far beyond the human limit during this research program. Movement of the vast quantities of (dry and wet) sand used in the numerous physical tests conducted in the Hydraulics Laboratory was possibly the most laborious experience I have ever encountered. I am therefore, and particularly, thankful to my colleagues (Marta López, Jeffrey Ma and Amanj Jamal) and several undergraduate students who volunteered along with both University of Ottawa (Philippe St-Germain and Mathieu Toupin) and overseas interns (Sihame Mimid, Pierre Moreels, Claire Doerrer, Yann Boscher and Jeremy Bortolotti: University of Limoges, France, Bastien Flechoux: l’Ecole d’ingenieur du Cesi, France, Romain Pagniez: ICAM, France and Telse Bartens: Technical University of Braunschweig, Germany), and who have shared this burden with me.

Exposure to the construction environment has undeniably allowed me to appreciate the importance and level of expertise required for any physical work.

I would like to acknowledge the invitation offered by Professor Richard Bathurst and Dr. Greg Siemens from the Department of Civil Engineering at the Royal Military College, Canada, to discuss the design of the tensiometer-transducer devices used in their research. I would also like to express my appreciation to Mehdi Arezoomand who has provided me a version of his computer code which has helped me register the images that I have captured and Dr. Mohamed Abdallah who has helped me create and configure the VI Tasks using LabVIEW. I am also very pleased and thankful that my brother, Mohammed Al-Riffai, and my dear friends, Omar Elhamy and M’hammed Kilito, have helped me with some of the photography and lighting installations.

vi I would like to express my gratitude to the University of Ottawa and Ministry of Training, Colleges and Universities of Ontario for financial support through the Admissions Scholarship and Ontario Graduate Scholarship, respectively. Funding of the experimental program was made possible through the CRTI Grant “Vulnerability of Infrastructure to Extreme Loading”.

Last but not least, I would like to give my thanks to all my family, particularly my mother and father, Susan and Hussein, for their unconditional support, encouragement, patience, and their daily prayers. Thank you for always being there for me. This is in recognition to your love and affection and for being my first teachers. I dedicate all my efforts to you. God bless you.

viiRemerciements



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