Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The moisture content of road foundations plays an important role in the durability
of the pavement and the driving comfort of the road. After a pavement has been
completed, gradual moisture changes occur in the foundations until equilibrium
conditions can be reached, and this can have negative results if expansive clays,
for example, are present in the foundation. Pre-wetting of the foundation
material is seen as a method to minimilize moisture changes after construction,
but if the pavement was already completed, it would be very difficult to change or
alter the moisture content in the foundation, because water could then only be
applied to the shoulder areas of the road and horizontal infiltration in the soil is
exceptionally slow.
The research which is reported in this account was undertaken to determine
whether the process of electro-osmosis could be applied to accelerate water
infiltration underneath covered areas, as in, for example, road foundation
layers. Electro-osmosis, if found to be successful, has various advantages, of
which the most important is that it can be applied without stopping the normal
operations of the road.
This research was carried out on a mixture of G5 material (TRH14 classification)
and fine material in the form of clay with a low plasticity. Firstly, tests were
performed to determine the percentage of fines required. It was found that, if too
little fines were present infiltration did not occur, because moisture could flow
freely through the openings between the rough aggregate. Electro-osmosis also
had no effect on the rate of flow. The allocated amount of fines required to fill
sufficient openings was about 30% (TRH14 classification of mixture is G10).
Free flow was stopped and true infiltration occurred. Simultaneously, the rate of
infiltration could be accelerated with electro-osmosis. Furthermore, a two-dimensional model of a road was constructed with
electrodes placed on both sides, with the aim to determine the infiltration pattern
controlled by electro-osmosis and what the effect of the initial moisture content
would be on the process. Water was introduced to the one side of the model
road and the wetting of the foundation was investigated. If the electric current for
electro-osmosis was switched off, the infiltration was mainly vertical, as
expected, but with the current switched on, there was an obvious acceleration of
infiltration in the horizontal direction. As in the case of the initial tests, it was
found that electro-osmosis was not very successful to accelerate horizontal
infiltration at low percentages of fines. Furthermore, it was obvious that electroosmosis
was also more effective if the initial moisture content of the soil was low.
Low amounts of fines and high initial moisture contents had rather the electroosmotic
flow of water passing underneath the road as a result instead of
infiltration acceleration, with the result that the moisture content did not change
much.
The research thus showed that electro-osmosis is a possible manner in which
moisture could be conducted into the foundation layers of roads to increase the
moisture content if the appropriate amount of fines and moisture content were
present in the foundation material. Further research could still be carried out and
the materials in each case should be practically evaluated before this method
could be continued with. / AFRIKAANSE OPSOMMING: Die voginhoud van padfondamente speel ’n belangrike rol in die duursaamheid
van die plaveisel en die rygerief van die pad. Nadat ’n plaveisel voltooi is, vind
daar geleidelike vogverandering in die fondamente plaas totdat
ewewigstoestande bereik is, en dit kan nadelige gevolge inhou indien uitsettende
kleie byvoorbeeld in die fundament teenwoordig is. Voorafbenatting van die
fondamentmateriaal word gereken as ’n metode om vogveranderinge na
konstruksie te minimeer, maar indien die plaveisel reeds voltooi is, is dit baie
moeilik om die voginhoud in die fondament te verander of beheer omdat water
dan slegs buite die skouerareas van die pad toegedien kan word en horisontale
infiltrasie in grond uiters stadig is.
Die navorsing waaroor hierin verslag gedoen word, is onderneem om te bepaal
of die proses van elektro-osmose aangewend kan word om waterinfiltrasie onder
bedekte areas, soos byvoorbeeld padfondamentlae, te versnel. Elektro-osmose,
indien dit suksesvol blyk te wees, hou verskeie voordele in, waarvan die
belangrikste dat dit aangewend kan word sonder om die normale bedryf van die
pad te staak.
Die ondersoek is uitgevoer op ’n mengsel van G5 materiaal (TRH14 klassifikasie)
en fynstof in die vorm van klei met ’n lae plastisiteit. Eerstens is toetse uitgevoer
om die persentasie fynstof wat nodig is, te bepaal. Daar is bevind dat, indien te
min fynstof teenwoordig is, infiltrasie nie plaasvind nie aangesien water vryelik
deur die openinge tussen die growwe aggregaat kan vloei. Elektro-osmose het
ook geen effek op die vloeitempo gehad nie. Die aangewese hoeveelheid fynstof
om genoegsame openinge te vul was ongeveer 30% (TRH14 klassifikasie van
mengsel is G10). Vrye vloei is dan gestuit en ware infiltrasie het plaasgevind.
Terselfdertyd kon die tempo van infiltrasie versnel word met elektro-osmose. Voorts is ’n twee-dimensionele model van ’n pad gebou, met elektrodes aan
weerskante geplaas, met die doel om te bepaal of die infiltrasiepatroon deur
elektro-osmose beheer kon word en wat die effek van beginvoginhoud op die
proses sal wees. Water is aan een kant van die modelpad ingevoer en die
benatting van die fondament bestudeer. Indien die elektriese stroom vir elektroosmose
afgeskakel was, was die infiltrasie hoofsaaklik vertikaal, soos verwag,
maar met die stroom aangeskakel was daar duidelike versnelling van infiltrasie in
die horisontale rigting. Net soos in die geval van die aanvanklike toetse is bevind
dat elektro-osmose nie baie suksesvol was om horisontale infiltrasie te versnel by
lae persentasies fynstof nie. Dit het verder geblyk dat elektro-osmose ook meer
effektief was indien die aanvanklike voginhoud van die grond laag was. Lae
hoeveelhede fynstof en hoë aanvanklike voginhoude het eerder elektroosmotiese
deurvloei van water onderdeur die pad tot gevolg gehad as
infiltrasieversnelling, met die gevolg dat die voginhoud nie veel verander het nie.
Die navorsing het dus getoon dat elektro-osmose ’n moontlike wyse is waarop
water in die fondamentlae van paaie ingevoer kan word om die voginhoud te
verhoog indien die geskikte hoeveelheid fynstof en voginhoud in die
fondamentmateriaal teenwoordig is. Verdere navorsing kan nog uitgevoer word
en die materiale van elke geval sal prakties evalueer moet word voordat met die
metode voortgegaan kan word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16326 |
| Date | 12 1900 |
| Creators | Glatz, Thomas |
| Contributors | De Wet, M., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xviii, 97 leaves : ill. |
| Rights | University of Stellenbosch |
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