Investigating the Operational behaviour of a Double Curvature Arch Dam

94 Pages·2017·3.82 MB·English

FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT
DEPARTMENT OF CIVIL ENGINEERING
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INVESTIGATING THE OPERATIONAL BEHAVIOUR OF A

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DOUBLE CURVoATURE ARCH DAM

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i Zac James Prins
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Submitted in partial fulfillment of the requirements for the degree
M.Eng.
Civil Infrastructure Management and Maintenance
Supervisor: Professor Pilate Moyo
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The copyright of this thesis vests in the author. No
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quotation from it or information derived from it is to be

published without full acknowledgeement of the source.
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The thesis is to be used for private study or non-
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commercial research purposes only.

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Published by the Universit y of Cape Town (UCT) in terms
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of the non-exclusive license granted to UCT by the author.
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PLAGIARISM DECLARATION
I know the meaning of plagiarism and declare that all the work in the document, save
for that which is properly acknowledged, is my own. This thesis/dissertation has
been submitted to the Turnitin module (or equivalent similarity and originality
checking software) and I confirm that my supervisor has seen my report and any
concerns revealed by such have been resolved with my supervisor.
Signature Removed
Signature: ______________________
Date: 12 May 2017
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DEDICATION
To my loving family for their unwavering support.

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ABSTRACT
The safety of dams is crucial in ensuring the continual availability of water, safety of
the surrounding communities and infrastructure. Surveillance systems are
implemented to monitor the structural integrity of certain dams which have a safety
risk. The components and extent of the surveillance systems adopted depends on
many factors, which include the type of dam wall structure used to impound the
reservoir, geotechnical and environmental conditions.
The case study used for this thesis is Kouga Dam located in the Eastern Cape
Province of South Africa. It is a double curvature, concrete arch dam which supplies
water for domestic, irrigation, and industrial use to the Gamtoos River Valley and
Nelson Mandela Metropolitan. During construction the stability of the right flank was
questioned and subsequently remedial measures were taken in order to increase the
shear resistance of this flank. Previous dam safety evaluations also noted the
possibility of Alkali Silica Reaction (ASR) occurring within the structure which
resulted in concrete swelling and loss of strength. Due to these factors and the large
hazard potential rating associated with this dam, an intensive surveillance system
has been used to monitor the dam's behaviour during operation.
In this thesis the results of the surveillance system is analysed. A strong linear
relationship exists between the temperature loading and displacement response of
the dam wall. Changes in temperature initiate the response of the structure almost
instantaneously. A more complex relationship exists between hydrostatic loading and
the displacement response of the structure. A phase lag of approximately one to
three months is evident between these two variables. Since construction the
displacement and strain rates in the upstream (y) and upward (z) directions are
0.3mm/annum and 8.6µε/annum respectively. However, since 1989 there has been a
reduction in the average displacement and strain rates in all directions by
approximately 70%. This may suggest that the ASR has stabilized. The vertical
construction joints, especially the central and upper joints, are relatively open during
low water levels. The structure is found to transfer the imposed loading mainly to the
central foundation via dominant cantilever action. As a result the reaction forces on
the upper foundation have been found to be relatively low, lowering the risk of
potential shear failure of the right foundation. Small foundation movements of less
than 0.3mm have been observed within the foundation downstream of the dam wall
on the right flank. These movements are between 10 and 40m within the
foundations.

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ACKNOWLEDGEMENT
Firstly I would like to thank Professor Pilate Moyo for his supervision and guidance
throughout this thesis. Dr. Chris Oosthuizen for urging me to pursue postgraduate
studies and stoking my interest in dam engineering. As well as Patrick Bukenya for
his help in the field and during the write-up of the document.
I would also like to acknowledge the Department of Water and Sanitation, for
providing the means for further studies, allowing me to utilize invaluable information
and also my fellow colleagues who assisted with the research.
Lastly, I would like to thank my family for their continuous support.

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TABLE OF CONTENTS
Plagiarism Declaration .............................................................................................. i
Dedication ................................................................................................................. ii
Abstract .................................................................................................................... iii
Acknowledgement................................................................................................... iv
Table of Contents ..................................................................................................... v
List of Tables ......................................................................................................... viii
List of Figures ......................................................................................................... ix
List of Abbreviations ............................................................................................... xi
Nomenclature ......................................................................................................... xii
Chapter 1 ................................................................................................................... 1
1 Introduction .................................................................................................... 1
1.1 Background ................................................................................................ 1
1.2 Problem Statement ..................................................................................... 2
1.3 Objective..................................................................................................... 2
1.4 Limitations and Scope of Research ............................................................ 2
1.5 Thesis Structure ......................................................................................... 2
Chapter 2 ................................................................................................................... 4
2 Design, Construction, and Management of Arch Dams: A Review ........... 4
2.1 Design of arch dams ................................................................................... 4
2.1.1 Brief historical review ................................................................... 4
2.1.2 Site considerations....................................................................... 4
2.1.3 Loading ........................................................................................ 5
2.1.4 Analysis ....................................................................................... 6
2.2 Construction of arch dams .......................................................................... 9
2.3 Management of arch dams ....................................................................... 10
2.3.1 Purpose (Statutory requirements) .............................................. 10
2.3.2 Structural response .................................................................... 11
2.3.3 Failure modes ............................................................................ 15
2.3.4 Alkali Silica Reaction .................................................................. 20
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2.3.5 Instrumentation .......................................................................... 23
2.4 Chapter Summary .................................................................................... 24
Chapter 3 ................................................................................................................. 25
3 Methodology ................................................................................................ 25
3.1 Introduction ............................................................................................... 25
3.2 Kouga Dam ............................................................................................... 25
3.2.1 Locality ....................................................................................... 25
3.2.2 Dam Characteristics ................................................................... 26
3.2.3 Background ................................................................................ 27
3.2.4 Geology ..................................................................................... 28
3.2.5 Right flank foundation conditions ............................................... 29
3.2.6 Loading on right flank foundation ............................................... 31
3.3 Monitoring System .................................................................................... 33
3.3.1 Overview .................................................................................... 33
3.3.2 Water Levels .............................................................................. 33
3.3.3 Temperature .............................................................................. 33
3.3.4 Displacements ........................................................................... 34
3.3.5 Ambient Vibration Measurements .............................................. 38
3.4 Chapter Summary .................................................................................... 42
Chapter 4 ................................................................................................................. 43
4 Results and Discussion .............................................................................. 43
4.1 Introduction ............................................................................................... 43
4.2 Instrumentation Data Results ................................................................... 43
4.2.1 Water Levels .............................................................................. 43
4.2.2 Temperature .............................................................................. 44
4.2.3 Geodetic Data ............................................................................ 45
4.2.4 GNSS/GPS Data........................................................................ 51
4.2.5 GNSS/GPS and Water Level ..................................................... 52
4.2.6 GNSS/GPS and Temperature .................................................... 54
4.2.6 Trivec System ............................................................................ 55
4.2.7 AVM and Water Level ................................................................ 57
4.2.8 Crack widths .............................................................................. 59
4.3 Comparative Study ................................................................................... 61
4.4 Dam Forces on Foundation ...................................................................... 62
4.5 Chapter Summary .................................................................................... 63
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Chapter 5 ................................................................................................................. 64
5 Conclusion and Recommendations ........................................................... 64
5.1 Summary .................................................................................................. 64
5.2 Conclusion ................................................................................................ 64
5.3 Recommendations .................................................................................... 65
References .............................................................................................................. 66
Appendices ............................................................................................................. 70
A. Trivec results ............................................................................................... 70

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LIST OF TABLES
Table 1: Typical static and dynamic loads on dams ................................................... 6
Table 2: Size classification ....................................................................................... 10
Table 3: Hazard potential classification .................................................................... 10
Table 4: Category classification of dams with a safety risk ...................................... 10
Table 5: Damping in concrete arch dams (USACE, 1994: 7-11) .............................. 13
Table 6: Operational Failure Modes of Dams ........................................................... 16
Table 7: Affect of ASR on concrete at 28 days (Oberholster, 2009: 211) ................. 23
Table 8: Investigated parameters ............................................................................. 33
Table 9: Installation levels and height of Trivec systems.......................................... 38
Table 10: Summary of displacement and strain rates .............................................. 50
Table 11: Trivec data summary ................................................................................ 57
Table 12: Crack width measurement periods ........................................................... 59
Table 13: Comparative dam statistics ...................................................................... 61

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