Geofabrics are incorporated in geotechnical engineering structures for various reasons and functions. This study addresses the reinforcement function whereby geotextiles are utilised as reinforcing elements in reinforced slopes and fills. It particularly focuses on the soil/geotextile interface behaviour. Geotextile reinforcements transfer a majority of the shear stress from the soil to the reinforcement and vice versa by friction. This interfacing ability manifested by the soil/geotextile frictional contact is very important in the performance of reinforced soil structures, and depends on the physical characteristics of the backfill as well as the geotextile. In this investigation, the interaction behaviour of geotextiles with sand is evaluated by conducting extensive laboratory interface tests both in direct shear and pull-out. A comprehensive test program was established to include a needle punched non-woven geotextile interacting with sands of different grading, grain size distributions and grain shapes namely; Cape Flats, Klipheuwel and Munich sands. The respective responses were primarily presented in terms of shear stress/horizontal displacement and pUll-out resistance/front displacement relationships; showing the frictional performance of the geotextile in these sands of different physical characteristics. Interface shear strength in both test methods was determined using Mohr-Coulomb's law. The ensuing shear strength values were compared with each other and with the direct shear strengths of the respective sands used in this investigation Specific emphasis and detailed analyses went into the pull-out experiments in which local displacements of the geotextile specimens were measured as the test progressed. The measurements enabled the study of the stretching characteristics of the geofabric in the different sands. Applying an extrapolation procedure to approximate the constantly changing deformation modulus of the geotextile as it stretched in the respective sands, allowed the back-prediction of the pull-out force/displacement relationship, and thus enabled the study of skin friction distribution along the geotextile specimen during pull-out. The effect of the grading and grain size on the development of the interface shear stress, the peak values, and the type of interface failure could be demonstrated. The analysis of the skin friction along the geotextile specimen led to the development of a generalised shear stress distribution graph which, if validated in further research, may be adopted in practical design situations. In a design example, it was shown that the assumption of interface shear parameters based on direct shear tests provides too optimistic a factor of safety. This study recommends the use of interface shear parameters derived from pull-out tests. The in-depth analysis of the tests in a variety of sands showed clearly that the shear stress is not uniformly distributed over the embedment length of the reinforcement. This skin friction drops dramatically from a peak value near the loaded end to zero at the free end in all investigated confinements.

With ever more pressure being exerted on South Africa to reduce its carbon emissions and their sole energy producer, Eskom, on the verge of collapse, electricity cost in South Africa are set to increase drastically. It is therefore important that electrical consumption be reduced throughout all sectors and wastewater treatment is no exception. With reduction of electrical consumption of WWTPs in mind, this thesis focused on the costing and viability of replacing less efficient aeration technology (slow speed surface aeration) with more efficient technology (fine bubble diffused aeration). The main objective of the investigation was to calculate the total cost (capital, maintenance and operational) of the two technologies, with the input of the varying inflow rates and wastewater characteristics, and find the inflow rate where the total cost of the two technologies are the same. This intersection was titled the Viability Threshold Point. With this point known it is possible to advise designers and investors as to when and where which aeration technology should be implemented. Different data groups were established with varying wastewater characteristics (see table below) as well as inflow rates varying from 1.0 Mℓ/d to 12.0 Mℓ/d. An inflow COD concentration of 750 mg/ℓ was chosen as a benchmark group and the other inflow characteristics were calculated to represent typical values based on this COD concentration.

Includes abstract. Includes bibliographical references (p. 209-217).

Includes bibliography. / Two of the main factors affecting the durability of reinforced concrete structures are the level of chlorides required to initiate corrosion and the subsequent rate of penetration of chloride ions through concrete. The primary focus of the current work is the study of how cement extenders impact on the corrosion characteristics of embedded steel in concrete. The investigation was limited to those materials commonly used in South Africa (slag, fly ash,and condensed silica fume) and performed under laboratory conditions at 30°C.

Summary in English. / Bibliography: leaves 5.1-5.7. / Biological nutrient removal activated sludge (BNRAS) systems have become the preferred treatment system for advanced municipal wastewater treatment in South Africa. They have proven to be cost-effective systems that produce effluents of excellent quality that can be re-introduced to the receiving water bodies without a significant negative impact on the scarce surface water of South Africa. The widespread implementation of the BNRAS system has drawn attention to some of the weaknesses of the system, predominantly (i) the long sludge ages and resulting large biological reactor volumes required for nitrification, (ii) filamentous organism bulking of the sludge that develops in the system, (iii) treatment of the P rich waste sludge from the system and (iv) containment of the large mass of P in the sludge during a failure of the aeration in the system. In order to overcome the first two weaknesses of the system, it is proposed to separate the process of nitrification from the BNRAS mixed liquor and achieve nitrification externally to the BNRAS system.

Includes abstract. / Includes bibliographical references. / Apartheid has left an urban legacy with excessive commuting distances for low income workers. Climate Change and Peak Oil will cause transport costs to rise. „Low carbon‟ solutions are not viable in developing cities such as Cape Town, where most workers already use public transport and it is unlikely that governments will have the resources to further subsidise increasing transport costs. Consequently, a proposal to restructure the city to reduce travel distance between work, home and recreational activities will assist the poor but also mitigate climate change. Cities in developing countries are expected to double in population over the next 25 years. This provides the opportunity to plan new settlements to reduce the dependency on motorised travel. This study seeks to explore one specific dimension of the costs and benefits of city restructuring: the perceived costs and benefits to employers of reduced employee catchments and whether there is “a point where increasing the size of the catchment of employees does not produce additional benefits to the employer.” Interviews were conducted with 47 managers of large Cape Town companies. A stated preference questionnaire was compiled to identify the trade-offs that employers make when faced with recruitment decisions. The costs were presented as a proportion of the company‟s current recruitment pool, the average distance travelled by employees per day, the change in environmental impact (CO2 emissions) of staff commuting and the financial cost of employee travel to the business (comprised of transport subsidies and carbon tax).Employees were divided into two groups. “Level 1” were low to lower-middle income staff (earning R3 000 – R10 000 per month) and “Level 2” were middle income staff (earning R10 001 – R30 000 per month). A Multinomial Logit (MNL) model was used to analyse the Level 1 and Level 2 data separately in terms of employers‟ utility. Results showed that an inflection occurs in employers‟ perceived value of catchment size and indicates a possible range at which this occurs. For employers recruiting Level 1, this inflection occurs at approximately 50% of the current recruitment pool and 15km radius. For Level 2 staff, this point of inflection would be approximately 55% of their current recruitment pool and 15km radius. Employers also emphasised the importance of low cost public transport to their business. As travel costs inevitably rise, reducing travel distances may become the only viable and long term solution. To become a viable solution, employers‟ fears must be understood and overcome. Denser and more integrated settlements around business hubs need to be presented as a win-win for environmental, social and economic sustainability.

Includes abstract. / Includes bibliographical references (leaves 127-133). / Material savings, cost effectiveness, weight reduction, Strength and aesthetics of steel structures are some of the key factors to be considered in structural design. In the last decade, non-prismatic steel members have proved to be more effective in structural design than the prismatic members, i.e. they have higher load carrying capacity when their geometry closely resemble the bending moment envelope as compared to prismatic members with the same material properties, loading and boundary conditions. However, there is a unique point (degree of non-uniformity) for which every non-prismatic member loses its load carrying capacity due to a change in its failure position and mechanism. Therefore, in order to investigate the effect of geometrical non-uniformity on steel members, non-prismatic steel members with different steel sections were simulated using ADINA/M 8.4.2 version whose function is based on finite element method. Furthermore, the non-prismatic steel members were modeled under different geometrical arrangements, degree of non-uniformity, boundary and loading conditions. Deflections, stress distributions, torsional effect and critical buckling load were recorded. The numerical results obtained in this study combine effectively an optimized check for different geometrical arrangements and degree of non-uniformity leading to a relatively improved economic and safe design.

Includes abstract. / Includes bibliographical references. / This document underscores various temperature related components and procedures for undertaking a successful performance analysis of concrete arch dams. Arch dams experience high temperature variations, which are generally assessed using finite element models. Deterioration of arch dams is caused principally by thermal effects, with 19% cases attributed to freezing and thawing, and 9% to temperature variations (Daoudu et al., 1997). The temperature loading conditions cause a high expanse of stresses at the various interface locations due to change in environmental conditions. Past research has shown that stresses caused by temperature change can be larger than those from reservoir loading (Bureau of Reclamation, 1977). The proposed finite element model for this study focuses on the performance assessment of arch dams in operation due to thermal loading.

Includes abastract. / Includes bibliographical references. / The purpose of this study was to create a framework for the development of a probabilistic model for durability design of reinforced concrete (RC) structures in South African marine conditions. Durability design of RC structures is mainly concerned with ensuring the ability of the concrete to resist the penetration of aggressive agents during the concrete‘s intended service life. RC structures in the marine environment may be attacked by aggressive chloride ions which penetrate concrete mainly through the diffusion mechanism. The chloride ions accumulate at the steel level and, upon reaching a critical concentration, cause corrosion to initiate which if not intercepted leads to the eventual deterioration of the entire structure.

Includes abstract. / Includes bibliographical references. / Although exhibiting many superior properties to open sections structural hollow sections (SHS) have seen limited application in structures where joints resist moments. Their application has remained largely in truss type and lattice type structures where pinned joints are assumed. However, SHS have wide potential for use in structures with moment resisting joints. Much still needs to be done, however, to develop an understanding of joint behaviour under moment loads. It is also desirable to come up with means of developing design tables that can simply the design process. The purpose of the research was to investigate the behavior of SHS joints under moment loading through experimental tests as well as using finite element modeling.