Unpaved roads comprise about 72 percent of the national and provincial
road network in South Africa and substantially more of the total
southern African road network. Significant costs are incurred annually
by the authorities on the maintenance of these roads and enormous sums
are associated with the cost of using these roads. Specifications for
the use of materials for unpaved roads in southern Africa abound, the
origin of most of these, however being rather obscure. It would appear
that many of them have been transferred from other countries, mostly
in the northern hemisphere.
The geological materials used for construction in southern Africa,
having been subjected to aeons of weathering and minimal major periods
of recent glaciation, differ greatly from those in the northern
hemisphere. One of the main objectives of this research was to
investigate the performance of local geological materials used in
wearing courses for unpaved roads and relate this to their
geotechnical properties. This involved the sampling, testing and
monitoring of 110 sections of unpaved road in the Transvaal and South
West Africa over a period of more than three years. A large data base
of gravel height, roughness, rut and corrugation measurements and the
severity and extent of dustiness, stoniness, potholes, cracks, loose
material, slipperiness and trafficability was compiled.
The material and performance data were then used to develop
performance related specifications and prediction models for roughness
progression and gravel loss with the aim of providing improved unpaved
roads and consequently reducing the road user and maintenance costs,
in the national interest. Some of the savings will obviously be
off-set to some extent by slightly increased materials location and
construction costs. These costs are, however, shown to be minimal in
comparison with the potential savings to the road user, the national
economy and the generally improved quality of life of many road users
in southern Africa. A good knowledge of the geotechnical properties of
potential wearing course materials (which are significantly dependent
on the geological origin) is necessary to differentiate good gravels
from poor ones.
Ongeplaveide paaie maak ongeveer 72 persent uit van die nasionale en
provinsiale padnetwerk in Suid Afrika en heelwat meer van die totale
padnetwerk van suidelike Afrika. Groot kostes word jaarliks aangegaan
deur die owerhede vir die instandhouding van hierdie paaie, asook
enorme kosts wat in verband gebring kan word met die gebruik van
hierdie paaie. Materiaalspesifikasies vir ongeplaveide paaie in
suidelike Afrika is volop. Die oorsprong van die meeste hiervan is
egter twyfelagtig en dit wil voorkom of dit uit ander lande,
hoofsaaklik in die noordelike halfrond, afkomstig is.
Die geologiese materiale gebruik vir padkonstruksie in suidelike
Afrika verskil grootliks van die in die noordelike halfrond. Dit was
onderwerp aan eeue se verwering en minimale groot-skaalse onlangse
glasiale werking verskil grootliks van die. Een van die hoof doelwitte
van hierdie navorsing was om ondersoek in te stel na die
werkverrigting van plaaslike geologiese materiale wat gebruik word vir
die slytlaag van ongeplaveide paaie en om dit in verband te bring met
hul Geotegniese eienskappe. Dit het behels monsterneming en toets van
materiale, asook monitering van 110 seksies ongeplaveide pad in
Transvaal en Suid-Wes Afrika oor 'n tydperk van drie jaar. 'n Groot
databasis bestaande uit inligting oor metings van gruishoogte,
ongelykheid, spoor en sinkplaat asook inligting van graad en omvang
van stof, klipperigheid, slaggate, krake, los materiaal, glibberigheid
en rybaarheid is saamgestel.
Die materiaal- en werkverrigtingsdata is toe gebruik om
werkverrigtingsverwante spesifikasies op te stel, asook om modelle
daar te stel om verswakking in gelykheid, en gruisverlies te voorspel.
Die doel is om beter ongeplaveide paaie te voorsien en gevolglik die
padverbruikers- en onderhoudskoste in nasionale belang te verminder.
'n Gedeelte van die besparing sal onvermydelik deur effens duurder
konatruksiekoste en moontlike langer vervoerafstande van materiaal
gekanselleer word. Hiedie koste is egter minimaal in verhouding tot
die potensiele besparing vir die padgebruiker, die nasionale ekonomie
en die algemene verbetering in lewenskwaliteit van baie padgebruikers in suidelike Afrika. 'n Goeie kennis van die geotegniese eienskappe
van potensiele slytlaagmateriale (wat grootliks afhanklik is van
geologiese oorsprong) is noodsaaklik om te differensieer tussen goeie
an swak gruise.
