Probabilistic safety analysis of dams [Elektronische Ressource] : methods and applications / by Negede Abate Kassa

Negede

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• Publié par: technische_universitat_dresden
• Publié le: 01 janvier 2009
• Nombre de lectures: 47
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

PROBABILISTIC SAFETY ANALYSIS OF DAMS
Methods and Applications







By

Negede Abate Kassa






Dissertation

submitted to Faculty of Civil Engineering
of Technische Universität Dresden
in partial fulfillment of the requirements
for the degree of





Doctor of Engineering (Dr.-Ing.)








TECHNISCHE UNIVERSITÄT DRESDEN



Dresden, Germany 2009






















© 2009 Negede A. Kassa, All Rights Reserved












Rigorosum, Demonstration und Disputation: 29.04.2010

Vorsitzender der Promotionskommission:
Prof. Dr.-Ing. Peer Haller (TU Dresden)

Gutachter:
Univ.-Prof. (em.) Dr.-Ing. habil. Hans-B. Horlacher (TU Dresden)
Prof. Dr.-Ing. Jürgen Jensen (Universität Siegen)


PROBABILISTISCHE SICHERHEITSANALYSE VON DÄMMEN
Methoden und Anwendungen







Dissertation


vorgelegt von


Negede Abate Kassa, M.Sc.



an der Fakultät Bauingenieurwesen
der Technischen Universität Dresden
zur Erlangung der Würde eines
Doktor-Ingenieurs (Dr.-Ing.)
















TECHNISCHE UNIVERSITÄT DRESDEN


Dresden, Germany 2009





















© 2009 Negede A. Kassa, All Rights Reserved





I dedicate this dissertation to my wife Abrehet.


iiiAcknowledgements
ACKNOWLEDGEMENTS
I would like to thank my supervisor Univ.-Prof. Dr.-Ing. habil. Hans-B. Horlacher for
giving me the opportunity to do this PhD under his supervision, for his invaluable advices and
continuous supports of all kind throughout the research period. It would not have been possible
for me to complete this PhD with out his resourcefulness and help – I owe you a big thank you
Prof. Horlacher! My thanks also go to my second supervisor Prof. Dr.-Ing. Jürgen Jensen for
volunteering to give his expertise as a co-supervisor and for his constructive comments. Thanks
are also due to members of the PhD examination committee for offering their expertise and time.

This dissertation is a result of the research work that was carried out mainly at the
Institute of Hydraulic Engineering/Institut für Wasserbau und Technische Hydromechanik
(IWD), Faculty of Civil Engineering/Fakultät Bauingieurwesen of Dresden University of
Technology/Technische Unibesrsität Dresden (TUD), where I have benefited a lot from the
inspiring and friendly atmosphere. Thanks are due to all members of the Institute. I, especially,
acknowledge the support I got from Dipl.-Ing. Torsten Heyer, Dipl.-Ing. Herbert Martin, Dipl.-
Ing. Holger Haufe, Dipl.-Ing. Sophia Stoebenau, Mrs. Kerstin Winkel and Mrs. Carola Luckner.

This research work is financially supported mainly from The United Nations
Development Program Second Country Co-operation Framework (UNDP-CCF2) project under
the framework of the support to Ministry of Water Resources (MoWR), Ethiopia. The field work
got financial assistance from Gessellschaft für Technische Zusammenarbeit/German Technical
Cooperation (GTZ). Financial support for attending conferences was availed by IWD-TUD.
Moreover, during the last year of the study funding was possible through a research assistant
employment I got at IWD-TUD. The funding from all sources is deeply acknowledged.

Data used for the case study of this research were obtained from National Meteorological
Service and MoWR, Ethiopia. Their co-operation is deeply acknowledged. I am grateful to Ato
Girma Mekonnen and Ato Abreham Assefa for hosting and supporting the laboratory work in the
Construction Design S.Co. Materials Testing and Foundation Investigation Laboratory. Thanks
are due to Wt. Yodit Ayallew, Ato Dercho Duelo, Ato Melaku H\michael, and Ato Yeshiyanew
Alemu for their help in field and at Arba Minch University soil mechanics laboratory.

Especially, I cannot say enough thank you to my hero and love- my wife Abrehet, for her
continuous support and encouragement all along. My gratitude goes also for her help in
reviewing the dissertation draft and to her useful advice on mathematics and computing. Thanks
Abisho! My lovely daughter Liyou you are my inspiration. I am sure this will double with Ruh’s
birth. My parents have always a special place in my life. I cannot thank you enough Bitish and
Abate for being good and loving parents to me. If I possess any good qualities, it is all because of
you. My brothers and sister, I owe you a big thank you for your supports and love all along.

I should not finish without expressing my gratitude to my Ethiopian and German friends
in Dresden (Anteneh, Taddele, Bahlbi, Mesfin, Doreen, Nigussie, Bini, Dr. Webtaye, Kelemwa,
Alemayehu, Alemash, Falk, Bederu and Tsedeke). So much fun and good times I have shared
with you. Thank you for all your supports and comforts. You made my stays in Dresden lively.

Negede Abate, August 2009.
vPreface

PREFACE
The safety of dam is inseparable from its foundation performance, its spillway capacity
and hydraulic characteristics and its integrity against seepage and destructive floods. In the past,
when sites were favorable and resources plentiful, the shortcomings of science were overcome by
generous budgets. Massive dams stand today as monuments to that era. Many of those works may
outlive the present civilization, surviving probable maximum floods, maximum earthquakes, and
an inevitable measure of neglect. They were sound investments in their time. Today, greater
emphasis must be placed upon the economical use of resources. Design criteria and rehabilitation
decisions must be scrutinized to eliminate excess use of resources whilst the provision of
adequate safety is assured. Enhancing dam safety increases investment costs and its decrease
boost potential risk, thus some balance must be found between the two conflicting interests
(economy and safety). It is necessary to determine levels of acceptable risk for different sets of
conditions; criterion for the design of proposed dams and rehabilitation of old dams must be
objectively justified. This calls for analytical risk and dam safety analysis.

The safety evaluation of aging dams and risk-based (probabilistic) design of new dams is
getting increased attention more than ever before. The public and decision makers now demand
transparency and accuracy in design decisions regarding safety issues of dams. Engineers are
more and more required to explicitly quantify risk-levels associated with designed dimensions of
new dams and upgrading or rehabilitation recommendations of old dams. They are required to
quantify how safe a dam is and how well the balance between safety and economy is kept; as
specified by engineering, societal, environmental, political and economical standards or
regulations. It is required to base such evaluations on numerical justifications derived from
transparent procedures that are well founded on theory than subjective judgment. However, this is
a complex undertaking because of uncertainties associated with parameters involved in dam
design; such as uncertainty in occurrence of loads and hazards, material property, geology,
models and boundary conditions, operators’ inputs, maintenance etc. Most physical and
operational variables in dam design are uncertain parameters. Nominal magnitudes assumed in
design are likely to differ in time and/or space and thus performance (capacity and safety) of
dams is too an uncertain parameter.

Traditionally uncertainty in design parameters is assumed to be accounted for through the
use of safety factors. By assigning generous safety factors dam performance (capacity and safety)
is assumed to remain in an acceptable range and it is customarily presumed that dams never fail.
Nowadays, in most modern engineering codes and society, the appropriateness of the safety
factor approach is being questioned. This approach does not allow for transparent accounting of
uncertainties and for numerical quantification of safety. It does not permit for optimizing safety
and economy uniformly across the system by associating a quantified level of risk to alternative
design options. Sometimes, if design is complex, safety factors can compound to cause over
design in certain parts of dams safety chain, with still one or more weak links and uncertain
reliability left unseen in other elements of the safety chain, ultimately living the system only as
safe as the weakest element in the chain. The safety factor method is only capable of giving
qualitative measurement. If engineers want to deal with variability of design parameters head-on
an