A thesis submitted to the Faculty of Engineering and Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of Doctor of Philosophy, 2017 / The effect of internal erosion on the mechanical behaviour of soils was investigated experimentally, using sodium chloride grains as an analogue for erodible soil grains. With this technique, the loss of controlled quantities of finer particles could be simulated under more realistic hydro-mechanical conditions than in previous research, but within practical experimental time scales. Two experimental programs were undertaken. The first looked at general changes in volume and shear strength using a large diameter oedometer adapted to perform a punch test following salt dissolution. The second program investigated particular changes in volume and shear strength following salt dissolution using an adapted direct shear box Previous studies have shown shear strength reductions following the loss of finer particles representing as little as 5 % of the total mass of the original soil. Findings here show shear strength can be largely unaffected if the erodible finer fraction (F) makes up less than a transition value (Ft) of approximately 10 – 15 % by mass of the original soil. This threshold represents F above which the coarser fabric is looser than at its minimum void ratio. As F increases further, finer particles increasingly hinder the coarser particles from achieving their densest packing, such that the coarser fabric remaining after finer particle loss is in a looser state than the original fabric, the remaining fabric reaching its maximum void ratio at a critical finer fraction (Fc) of approximately 25 – 35 %. For F < Fc, finer particle loss results in limited collapse of the coarser fabric and it was found that the state of this initial coarser fabric determines the shear behaviour of the soil following the loss of finer particles. The shear behaviour of initially dense specimens with F < Ft remained similar to that of a dense soil following finer particle loss, whereas shear behaviour of initially dense specimens with Ft < F < Fc approached that of a loose soil as F increased. Soils with higher internal filter ratios (D15c/D85f) were found to have higher values of Ft and Fc. Soils with F > Fc, settled and weakened significantly following finer particle loss, reflecting the load-bearing role finer particles play in this case. This load bearing nature of the finer particles in soils with F > Fc decreases the risk of internal erosion. / CK2018

No description available.

An instrumented oedometer was designed and constructed for the purpose of investigating at-rest and compaction-induced earth pressures in moist soils. The device has a split oedometer ring, and horizontal stresses are measured using load cells which support one half of the ring. Rapid cyclic loading was applied to compacted soil specimens, using a digital pressure regulator and a computer-based data acquisition system. The performance of the device was validated by performing tests on silicon rubber and Monterey sand. / Ph. D.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Microorganisms play an important role in the stability and maintenance of the ecosystem and in the condition of the soil. However, in their natural environment, microorganisms often experience changing and hostile conditions. They therefore need to be able to adapt physiologically and modify their micro-environment. Biofilm formation is one mechanism to establish favorable micro-environments. The extracellular polymeric substances (EPS) that are typically associated with biofilm formation may also have an impact on soil structure. The aim of this project was to evaluate the potential of microbial manipulation on EPS production and the possible impact thereof on soil structure in order to improve water retention. Specific objectives of this study included the screening of natural environments for EPS-producers, developing techniques to observe EPS production and accumulation in the pores between soil particles, measuring the effect of EPS production on soil water hydraulic gradient, as well as determining the fate and impact of EPS-producers when introduced to naturally-occurring soil microbial communities. Several environmental samples have been screened for EPS-producing microorganisms. Soil columns were then inoculated with these EPS-producers and the passage of 20 mlaliquots water through the columns measured at 3 or 4-day intervals. Microbes isolated from soil, through their EPS production capability proved to retain water more effectively than was the case for water-borne EPS-forming microbes. This phenomenon was further studied using flow cells, filled with soil and inoculated with the EPS-producers isolated from either soil or water. Fluorescence microscopy showed that the soil microbes produced EPS that clogged pores between sand particles more effectively. This clogging resulted in lowering the soil water hydraulic gradient. To evaluate the effect of EPS-producers on existing soil microbial communities, cell counts, Biolog™whole-community carbon utilization studies and T-RFLP (terminal-restriction fragment length polymorphism) analyses were performed. Shifts in the soil microbial community could not be readily seen by observing microbial numbers and T-RFLP-analysis, but was noticeable in carbon utilization patterns. / AFRIKAANSE OPSOMMING: Mikroorganismes speel 'n belangrike rol in die stabiliteit en instandhouding van die ekosisteem en in die kondisie van die grond. In hul natuurlike omgewing ervaar mikroorganismes dikwels veranderlike en ongunstige toestande. Mikroorganismes het dus nodig om hulself fisiologies aan te pas en verander hul mikro-omgewing daarvolgens. Biofilm-vorming is een meganisme om gunstige mikro-omgewings te skep. Die ekstrasellulêre polimeriese produkte (EPP) wat tydens biofilm-vorming gevorm word, mag ook 'n impak hê op die grondstruktuur. Die doel van hierdie projek was om die potensiaal van mikrobiese manipulasie op EPP-vorming te evalueer asook die moontlike impak daarvan op grondstruktuur wat sodoende waterretensie kon bevorder. Die spesifieke doelwitte van hierdie studie het ingesluit die isolasie van EPPproduseerders vanuit natuurlike omgewings, die ontwikkeling van verskeie tegnieke waarvolgens EPP-produksie en die akkumulasie daarvan in die porieë tussen gronddeeltjies bestudeer kon word, die effek van EPP-produksie op hidrouliese gradiënt van grondwater en om die lot en impak wat EPP-produseerders op natuurlike grondmikrobiese populasies te bepaal. Verskeie grond- en watermonsters was getoets vir die voorkoms van EPP-produserende mikroorganismes. Grondkolomme is geïnokuleer met EPP-produseerders en die vloei van 20 ml-volumes water deur die kolomme is gemeet met 3 of 4-dag intervalle. Grond-geïsoleerde mikrobes het beter waterretensie tot gevolg gehad as water- geïsoleerde mikrobes. Hierdie verskynsel was verder bestudeer deur die gebruik van vloeiselle, gevul met grond of sand en geïnokuleer met EPP-produseerders geïsoleer vanuit grond of water. Fluoressensie mikroskopie het aangetoon dat grondmikrobes EPP produseer wat die porieë tussen gronddeeltjies meer effektief verstop. Dié verstopping het gelei tot die verlaging van die grondwater se hidrouliese gradiënt wat bepaal is deur die gebruik van die konstante-vlak bepalingsmetode. Om die effek van EPP-produseerders op bestaande mikrobiese populasies te bepaal, is seltellings, Biolog™ heel-gemeenskap koolstofverbruik studies en T-RFLP (terminale-restriksie fragment-lengte polimorfisme) analises uitgevoer. Veranderinge in die mikrobiese populasie kon nie geredelik bloot deur die bepaling van mikrobiese getalle en T-RFLP-analise waargeneem word nie, maar wel met die koolstofverbruikspatrone.

published_or_final_version / abstract / Applied Geosciences / Master / Master of Science

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Applied Geosciences / Master / Master of Science

CSLIP2 (De Natale, 1987) is the only slope stability program that utilizes a "direction set" optimization routine in its search for the minimum safety factor. However, CSLIP2 which employs Powell's Conjugate Direction Method permits only the horizontal and vertical directions (x and y) to be used as the initial direction set. The efficiency of the existing search routine is improved by replacing the x-y coordinate directions with initial directions that are parallel to and perpendicular to the principal axis of the safety factor contours.

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg 1998. / Various studies have been done to show that labour-based construction can meet the high standards normally required in the construction of roads. The organisational requirements that were needed to ensure the efficient use of labour have also been dealt with in various studies. Tile need for alleviation of poverty, unemployment and the negative social impact thereof by increasing the labour input in construction is understood by all concerned. A further step is however necessary before the idea of increasing the . labour component in any kind of roadwork can be taken seriously. Engineers need to move forward from the policy and organisational issues associated with labour intensive construction and start to provide designers with sound and innovative engineering solutions to overcome the hurdles experienced on the ground. The study looks at the process of foam bitumen stabilisation of soils and gravels with a view of utilising this innovative method for labour intensive construction. The material after having been stabilised can be placed in a stockpile. Actual durations that the material can safely remain in stockpile have been determined in this study to be in excess of six months for recycled asphalt and in excess of four months for the foam stabilised sand. Foam stabilised gravel was also studied and showed that after a year in stockpile the material failed probably due to a weakening of the bitumen and aggregate bond. Covering the stockpiled material did not show any significant difference to that of a similar uncovered stockpile. The position within the stockpile also did not have much effect on the engineering properties of the stoc piled material. The fact that the foam stabilised material can be worked on when cold and that it can be stockpiled for several months implies that the material is labour friendly and can be used in labour intensive construction of road base course layers or wearing course layers. / AC2017

A project report submitted to the Faculty of Engineering, University of the Witwatersrand in partial fulfilment of the requirements for the degree of Master of Science in Engineering. / Until recently use of ionic chemical soil stabilisers seemed hit or miss. The paper by paige-Green and Bennett explains that the stabilisers work only on soils containing reactive clays. The author's findings confirm this conclusion. It was shown that a CBR test, which can be done in any road soils laboratory, can be used to measure the chanqe in strength caused by the treatment of the soil with a chosen ionic stabiliser. South Africa is faced with a serious unemployment problem. The World Bank and the International Labour Organisation have shown that employment in construction can be significantly increased by the use of labour instead of machinery. Field trials showed that ionic stabilisers can readily be applied labour intensively. These stabilisers could improve marginal materials to road-building standard and this could further reduce the dependence on machinery by reducing the need to transport quantities of high quality gravel. / Andrew Chakane 2019