1887

oa Civil Engineer in South Africa - Concrete waterway linings for the Drakensberg Pumped Storage Scheme

 

Abstract

Concrete lined waterways for the Drakensberg Pumped Storage Scheme total about 8,5 km in length while there is also a length of about 1 km of steel lined penstocks. The overall alignment of the waterways was dictated by the topography of the site and economic considerations. Detailed vertical and horizontal alignments were however influenced by local geology and by operating requirements.


In general the design of the low pressure linings did not present unusual problems and the low permeability of the rock justified the adoption of unreinforced concrete linings. The presence of degradable mudstones in the geological sequence did however require special measures to be taken to avoid erosion of material from behind the linings.
For the high pressure linings the most economical and technically acceptable design involved prestressing of such linings by contact grouting to prevent the introduction of water into the rock mass. This solution resulted in a composite rock / concrete structure which acts elastically throughout the range of loading.
The combination of relatively low rock moduli and high internal pressures resulted in these linings being, as far as is known, the most highly stressed in the world. The paper describes the factors considered in the design and the techniques adopted to achieve satisfactory stressing. Operational experience shows that the design requirements have been achieved.
Steel linings were adopted in the area of relatively low overburden stress where leakage of high pressure water could result in areal hydrofracture of the rock which could not be tolerated. The paper briefly describes the factors considered in the design of those linings and the cut-off and drainage arrangements adopted to prevent the possible migration of water from the concrete lined high pressure waterways upstream of the steel linings towards the power station complex.

Die lengte van die betonbekledewaterweë vir die Drakensberg Pompopgaarskema beloop ongeveer 8,5 km, terwyl daar ook omtrent 1 km staalbeklede tonnels is. Die globale belyning van die waterweë is deur die topografie en ekonomiese faktore bepaal. Die finale belyning is egter deur geologiese omstandighede en bedryfsoorwegings beïnvloed.


Ontwerp van die laagdruktonnelvoerings het oor die algemeen geen ongewone probleme opgelewer nie en die lae deurlatendheid van die gesteentes het die gebruik van onbewapende betonvoerings regverdig. Die teenwoordigheid van swak moddersteen in die geologiese opeenvolging het egter genoodsaak dat spesiale maatreëls getref moes word om erosie van verweerde materiaal van agter die voering en verlies aan rotsondersteuning vir die voering te voorkom.
Die mees ekonomies en tegnies aanvaarbare manier om te verhoed dat water onder hoë druk die rotsmassa agter die hoogdruk tonnelvoerings binnedring was om die bewapende betonvoerings voor te span deur middel van grensvlakbryvulling. Dit sou langtermyn rotsondersteuning vir die bekleding verseker en het tot gevolg gehad dat die voering en rots 'n saamgestelde struktuur beslaan wat tussen die belastingsgrense elasties vervorm. Die kombinasie van 'n betreklik vervormbare rotsmassa en hoë interne druk het egter tot gevolg dat die voorspanning in die voerings sover bekend die hoogste ter wêreld is. Die faktore wat in die ontwerp in ag geneem is en die tegnieke toegepas om te verseker dat voldoende voorspanning gedurende bryvulling behaal is, word in die referaat beskryf. Bedrysondervinding toon aan dat aan die vereistes van die ontwerp voldoen is.
Staalvoerings is verskaf in die sone van relatief laë bolaagdruk waar lekkasie van water onder hoë druk onaanvaarbare hidrouliese breuksplyting van die rots tot gevolg sou gehad het. Die faktore wat in die ontwerp van die staalvoerings in aanmerking geneem is en die rangskikking van die syferversperring en dreineringstelsel benodig om moontlike syfering van water van die betonbeklede waterweë stroomop van die staalvoerings na die kragstasiekompleks te voorkom, is beskryf.

Loading

Article metrics loading...

/content/civeng1/24/8/EJC24888
1982-08-01
2016-12-03
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error