Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Large areas of the earth’s surface are covered by soils that are susceptible to large
decreases in bulk volume when they become saturated. These soils are termed
collapsing soils and are very common in parts of the USA, Asia, South America and
Southern Africa. This study is concerned with the occurrence of these collapsible soils
in the residual granites of the Stellenbosch area. The study was undertaken as
relatively little is known about the collapse phenomenon in the problematic weathered
granites of the Western Cape. The majority of research thus far has been carried out
on the deep residual soils formed on basement-granite in the Transvaal areas, whereas
little attention has been paid to the Cape granites.
The aim of the study was achieved through the experimental work which included
double oedometer testing, indicator analyses and shear strength testing. Double
oedometer tests were performed to quantify the potential collapse settlement of the
soils from the demarcated study area. To provide a better understanding of the
collapse behaviour of the soils, indicator analysis, which included Atterberg limits
and particle size distributions, were performed. Direct shear tests were further carried
out on saturated and natural moisture content specimens to establish the effect of
collapsibility on shear strength and whether substantial additional settlement of the
saturated soils would occur during shear.
It was found that collapsible soils are prevalent in the demarcated study area as the
majority of soils showed a potential collapse settlement of 1% or more. Collapse
exceeding 5% were calculated in a few instances proving some soils to be highly
collapsible. The double oedometer and indicator analysis results were used in an
attempt to obtain a relationship between collapse settlement and a combination of
easily determined properties such as dry density (void ratio), moisture content and
grading, but no meaningful conclusions have emerged. The shear strength tests
indicated that a clear correlation does not exist between collapsibility and shear
strength. It was further established that a relationship between collapse settlement
determined during the double oedometer testing and the volume change during shear strength testing cannot be assumed. It can thus be concluded that soils can be very
unpredictable and further research on the collapse phenomenon is indicated. / AFRIKAANSE OPSOMMING: Groot dele van die aarde se oppervlakte is bedek deur grondtipes wat geneig is tot ‘n
afname in volume as dit deurweek word. Hierdie gronde word swigversakkende
gronde genoem en dit word algemeen teëgekom in dele van die VSA, Asië, Suid-Amerika en
Suider-Afrika. In hierdie studie word die voorkoms van swigversakkende
gronde in die residuele graniet in die Stellenbosch area ondersoek. Die studie is
onderneem aangesien relatief min i.v.m. die swigversakking-verskynsel in die
problematiese verweerde graniet van die Weskaap bekend is. Die meeste van die
navorsing sover is onderneem op die diep residuele gronde wat gevorm is op die
Argaïese graniet in die Transvaal gebied, en betreklik min aandag is geskenk aan die
Kaapse graniet.
Tydens die studie is eksperimente wat dubbele oedometer toetse, indikator analises,
en skuifsterkte toetse insluit, uitgevoer. Dubbele oedometer toetse is uitgevoer om die
potensiële swigversakking van die grond in die afgebakende studiegebied te
kwantifiseer. In ‘n poging om die swigversakking-verskynsel van die grond beter te
verstaan, is indikator analises wat Atterberg grense en partikel grootte verspreiding
insluit, uitgevoer. Direkte skuiftoetse is ook uitgevoer op deurweekte grondmonsters
en op monsters wat natuurlike vog bevat, om sodoende die effek van swigversakking
op skuifsterkte vas te stel en om uit te vind of aansienlike addisionele sakking van die
deurweekte gronde tydens skuif plaasvind.
Daar is gevind dat swigversakkende gronde die oorheersende grondtipe in die
afgebakende studiegebied is waar meeste van die gronde ‘n potensiële swigversakking
van meer as 1% toon. ‘n Swigversakking van meer as 5% is in ‘n paar gevalle
bereken, wat bewys dat sommige grondtipes hoogs versakkend is. Die resultate van
die dubbele oedometer en indikator analises is gebruik in ‘n poging om te bewys dat
daar ‘n verhouding bestaan tussen swigversakking en ‘n kombinasie van kenmerke
wat maklik vasgestel kan word soos droë digdheid (ruimte verhouding), voginhoud en
gradering, maar daar kon nie tot ‘n sinvolle slotsom gekom word nie. Die skuifsterkte
toetse toon dat daar nie ‘n duidelike korrelasie bestaan tussen swigversakking en
skuifsterkte nie. Daar is verder vasgestel dat dit nie moontlik is om te aanvaar dat daar ‘n verhouding bestaan tussen swigversakking soos vasgestel tydens die dubbele
oedometer toetsing, en die verandering in volume tydens skuifsterkte toetsing nie.
Daar is dus tot die slotsom gekom dat grond baie onvoorspelbaar kan wees en dat
verdere navorsing na die swigversakking-verskynsel nodig is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5214 |
| Date | 12 1900 |
| Creators | Gildenhuys, Nanine |
| 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 | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 178 p. : ill. |
| Rights | University of Stellenbosch |
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