Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A trial closure of the emergency gate of the Berg River Dam was undertaken by the Trans-
Caledon Tunnel Authority (TCTA) on 12 June 2008. The air vent downstream of the emergency
gate was designed to introduce air to mitigate the negative pressures that were expected in the
conduit during emergency gate operations. The emergency gate has to close when the radial
gate at the downstream end of the outlet conduit fails. Contrary to the theoretical design, the
measured air vent velocities in the field indicated that, while the emergency gate was closing,
very large volumes of air were apparently continuously being released from the air vent,
commencing when the gate was about 30% closed (i.e. 70% open). This is in contrast to what
the design intended, namely that air should have been drawn into the vent.
This thesis is concerned with the testing of a 1:14.066 physical model representing the outlet
works and air vent of the Berg River Dam as a means to determine the reasons for the release
of large volumes of air from the air vent during the trial closure in 2008. It also seeks solutions to
mitigate the excessive airflow from the air vent. It was concluded that the air velocity in the air
vent was independent of the rate of closure of the emergency gate, but to increase with
increasing water head. The problem at the Berg River Dam was determined to be one of air
blowback. Modifications were made to the configuration of the model in order to determine whether the
configuration of the outlet works caused air to be released from the air vent. It was determined
that the downward sloping roof at the outlet of the conduit, used to accommodate the radial gate
chamber, was the cause of the air blowback phenomenon. An additional air vent was fitted
directly onto the conduit at the constriction was found to be ineffective in reducing the air
blowback. It was concluded that there are no rational structural change that can prevent or
inhibit a recurrence of the blowback phenomenon in the Berg River Dam outlet conduit.
The recommendation follows that the outlet conduit should not be constricted by any structural
or mechanism further downstream in the conduit. / AFRIKAANSE OPSOMMING: ʼn Toetssluiting van die noodsluis van die Bergrivierdam is op 12 Junie 2008 deur die TCTA
(Trans-Caledon Tunnel Authority) uitgevoer. Die lugskag stroomaf van die noodsluis is ontwerp
om lug in te voer om die verwagte negatiewe drukke tydens die noodsluissluiting te beperk. Die
noodsluis moet sluit indien die radiaalsluis aan die einde van die uitlaatpyp sou faal. In
teenstelling met die teoretiese ontwerp, het die gemete lugsnelhede in die lugskag in die veld
aangedui dat groot volumes lug voortdurend uit die lugskag vrygelaat word wanneer die
noodsluis ongeveer 30% toe is (dit wil sê 70% oop). Dit is in teenstelling met die ontwerp, want
die lugskag is ontwerp vir die insuig van lug.
Hierdie tesis het ten doel om die redes vir die vrylating van groot volumes lug uit die lugskag vas
te stel met behulp van ʼn 1:14.066 fisiese skaalmodel van die uitlaatwerke en lugskag van die
Bergrivierdam soos getoets tydens die inwydingstoetssluiting in 2008. Die toetse op die model
het getoon dat die lugsnelheid in die lugskag onafhankik van die sluistoemaak tyd is, maar
verhoog met die toename in die watervlak. Die Bergrivier dam probleem was bepaal as die van
lug terugslag.
Die model is gewysig ten einde te bepaal of die spesifieke samestelling van die uitlaatwerke die
oorsaak van die vrystelling van lug uit die lugskag is. Die analises en verandering aan die uitleg
toon aan dat die skuins afwaartse dak van die uitlaattonnel om die radiaalsluiskamer te huisves
die rede was vir die vrylating van die lug uit die lugskag. ‘n Addisionele lugskag was gebou in
die dak van die uitlaattonnel reg bo die sametrekking, maar was oneffektief om die terug vloei
van lug te verminder. Die gevolgtrekking is dat daar geen rasionele strukturele verandering
aangebring kan word aan die Bergrivier dam om die vrystelling van lug uit die lugskag te
verhoed of te verminder nie. ’n Aanbeveling vir toekomstige ontwerpe is dus dat die uitlaattonnel nie beperkend by die uitlaatend
moet wees nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71850 |
| Date | 12 1900 |
| Creators | Vos, Adele |
| Contributors | Basson, G. R., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 119 p. : ill. |
| Rights | Stellenbosch University |
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