Volume 23, Issue 6, 1981
Civil Engineer in South Africa - Volume 23, Issue 6, June 1981
Volume 23, Issue 6, June 1981
Metropolitan transportation : problems, projections and solutions
Author J.G. Brand
Source: Civil Engineer in South Africa 23, pp 231 –235 (1981)
Until a few years ago transportation studies were rather simple mechanical processes, usually yielding questionable proposals, with the result that expenditure in implementing transportation schemes ran the risk of being wasteful. Two elements of this problem are the difficulty of sampling and collating base land-use and transportation data and choosing or developing models which will realistically project the data to the target dates chosen.
In the Cape Town Study one of the difficulties encountered was that of effectively transferring data, aggregated in zones of homogeneous land-use, to traffic generation zones. Another difficulty was how best to deal with the socio-economic and travel characteristics of the non-white population. Because major unforeseeable incidents and developments such as fuel price increases, booms, depressions and changes in employment policies must have a tremendous influence on travel parameters, the outputs of projection models are often grossly inaccurate and of little real value.
A partial answer to this dilemma is to broaden the scope of forecasting to cover a spectrum of possible future situations rather than a unique one. A method now favoured is the use of scenario planning.
A further general problem is how best to optimize modal split between bus, train and private cars. A compromise between several conflicting factors must be sought In order to optimize the use of all the presently available and future proposed facilities.
Tot &apos;n aantal jare gelede was vervoerstudies taamlik eenvoudige meganiese prosesse wat gewoonlik twyfelagtige voorstelle tot gevolg gehad het, met die gevolg dat uitgawes aan die implementering van vervoerskemas verkwistend bestee mag word. Twee elemente van hierdie probleem is dle moeilikheid wat ondervind word in die monstering en vergelyking van basiese grondgebruik- en vervoerdata en die keuse of ontwikkeling van modelle wat die data realisties tot die gekose voorgenome datum sal projekteer.
In die Kaapstadse Vervoerstudie was een van die probleme wat ondervind is die van die doeltreffende oorplasing van data, byeengebring in sones van homogene grondgebruik, na verkeerverwekkingsones. Nog &apos;n probleem was hoe om die sosio-ekonomiese en reiskenmerke van die nie-blanke bevolking te hanteer. Omdat belangrike onvoorsienbare gebeure en ontwikkelinge soos brandstofprysverhogings, oplewing en daling van die ekonomie en veranderinge in indiensnemingsbeleid &apos;n geweldige invloed op reisneigings en gewoontes moet hê, is die resultate van projeksiemodelle dikwels uiters onakkuraat en van min werklike waarde.
&apos;n Gedeeltelike antwoord op hierdie probleem is om die omvang van die voorspelling te verbreed om &apos;n spektrum van toekomstige situasies, eerder as &apos;n enkele een, te dek. &apos;n Metode wat nou guns gewen het is die gebruik van scenario-beplanning.
&apos;n Ander algemene probleem is hoe om die modaleverdeling tussen bus, trein en private motors te optimaliseer. &apos;n Skikking tussen verskillende teenstrydige faktore moet gevind word ten einde die gunstige gebruik van al die huidig beskikbare en toekomstig voorgestelde geriewe te verkry.
Delvers Street cable tunnel : a geotechnical case study of predicted conditions
Author H.A.D. Kirsten
Source: Civil Engineer in South Africa 23, pp 237 –247 (1981)
The geological strata and tunnelling conditions with regard to excavation class, stand-up time and temporary support were predicted along the route of the Delvers Street tunnel. The actual conditions encountered are compared in detail in the paper with the expected conditions. The rates of advance and the costs of construction are also discussed briefly. The determination of dead and live loads on the permanent support is presented in some detail whilst the required design considerations are considered in principle only. In conclusion the cost of the geotechnical investigation, on which the Geological and Geotechnical Appendix to the Contract Document was based, is given in broad terms.
Service reservoirs of the Rand Water Board
Authors: F.S. Whitehead and R.J. Laburn
Source: Civil Engineer in South Africa 23, pp 249 –262 (1981)
The function of service reservoirs in the pumping and distribution systems of a bulk water supply undertaking and its consumers is described. The evolution and development since 1903 of the arrangement of service reservoirs for the Rand Water Board is set out and desirable design features and construction procedures listed.
Die funksie van diensreservoirs in die pomp- en distribusiestelsels van &apos;n onderneming wat water by die groot maat verskaf en van sy verbruikers word beskryf. Die evolusie en ontwikkeling van die rangskikking van diensreservoirs vir die Randwaterraad sedert 1903 asook die gewenste ontwerpkenmerke en konstruksieprosedures word uiteengesit.