Browsing by Author "Scheele, F"

Now showing 1 - 7 of 7
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    Considerations of mineralogy and permeability testing of selected Sand/Bentonite mixes
    (2008) Makgekgenene, Boné; Scheele, F
    The disposal of municipal, commercial and industrial waste contained in near impervious lining systems still poses challenges in terms of sustainability and long-term durability. This thesis assesses the engineering behaviour and chemical performance of selected Sand/Bentonite mixes to be used in the context of an environmentally inert landfill liner. Numerous test series in the laboratory focused on the permeability as a consequence of the physio-chemical characteristics of the selected mixes of two South African Bentonites and locally available sands. Several exploratory techniques (i.e., Cation Exchange Capacity; X-Ray Fluorescence; Scanning and Transmission Electron Microscopy) were employed to obtain the respective properties of the test materials. A flexible membrane test setup in connection with the falling head principle was used to determine the permeability of the mixes. A wide variety of bentonite percentage mixes (by mass) and a range of confinement pressures were investigated. The testing schedule catered for high and low compaction energy levels, hence covering a wide range of densities of the barrier material. The results of the exploratory techniques reveal valuable information on the quality and uniqueness of the two types of bentonites and allow comparative studies of their performance within a technical application. In the context of permeability, the grain size distribution, all round pressure, compaction, hydraulic gradient, quantity and distribution of bentonite within a mix contribute immensely towards the coefficient of permeability of any sand/bentonite mix. A visual presentation of the interrelationship of bentonite content, density of the mixes, confinement and coefficient of permeability is presented.
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    Constitutive modelling of the behaviour of clays under cyclic loading
    (1989) Sellers, E J; Scheele, F
    This research work involved the implementation of a constitutive model based on plasticity theory to model the behaviour of a clay under cyclic loading. The modelling must be based on an understanding of the soil response and the critical state theory provides a description of the soil response which then be formulated in terms of plasticity theory. A literature review showed that there is a shortage of information on the behaviour of soils under cyclic loading. Constitutive models for 'cyclic loading are discussed to compare the predictions and thus select a model.
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    Development of a constitutive model for a heaving clay from Rosebank
    (1993) Wiseman, K H; Martin, J B; Scheele, F
    Heaving clays are partially saturated soils composed of a high fraction of the montmorillonite clay mineral. When exposed to free water they undergo volumetric expansion, which often results in differential movements at the surface and damage to building structures founded on the clay. The economic consequences of such damage is severe. Heaving clay causes in excess of R100 million damage in South Africa each year, making it the country's most significant problem soil. The best method of dealing with a heaving clay is through appropriate design. This would be facilitated if methods such as finite element analysis were available to designers. The aim of this research project was to develop a constitutive model for an expansive clay which could be numerically implemented within the finite element method. A review of available literature on expansive clays showed that the heave strain that clay under an applied load will undergo can be expressed in terms of the parameters percent heave and heave pressure. These parameters are influenced by the degree of moisture changes experienced by the soil, and its dry density. Various different methods of establishing the percent heave and heave pressure have been proposed, but the values given by each differ due to the influence of different test stress paths on the results. More detailed examination of the effect of test stress path on the volume of heaving clays was therefore required to resolve the reasons for the differences in the test results, and to give a fuller understanding of the volumetric response of the material for the purposes of developing the constitutive model. Hence a series of laboratory tests was conducted on a clay from Rosebank in the Cape Province to investigate the effect of test stress path on the clay volume.
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    An experimental investigation of cyclically, axially loaded piles in sand
    (1993) Cowburn, S J; Scheele, F
    The research work involved the installation and cyclic load testing of large-scale pressure-grouted, instrumented piles in sand in the laboratory. The major objective of this experimental investigation was to establish the effects of the mean cyclic load level and amplitude on the pile behaviour during cyclic loading. Of particular interest was the study of the skin friction distributions along the pile shafts in order to understand the processes involved. Cyclic loading was limited to one-way loading in load-controlled mode. A literature review showed a lack of experimental data on the cyclic behaviour of large-scale pressure-grouted piles. The results of a number of small model tests in sand are discussed and the major trends of pile performances are highlighted to facilitate comparison of the observations made in this research. It was found that no definite testing procedure for cyclically-loaded piles is common to the various investigations. A research program and procedure of load applications was therefore developed to allow the isolation of the individual influences of the most significant cyclic parameters, the mean cyclic load level and the amplitude. In total 12 piles were installed using the same sand preparation and pile installation techniques. The tests only varied with regard to the applied loading procedure
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    An investigation of lateral support systems by the finite element method
    (1993) Clark, Troy Cedric; Scheele, F; Mitchell, G P
    The design of lateral support systems, in the context of surface excavations, are usually done using conventional (classical) methods of analysis. For these design procedures limit state assumptions are made concerning the lateral earth pressures acting on the structure to determine the support system characteristics. No information with regard to the deformation of the soil adjacent to the structure can be provided. The objective of this thesis is to examine the finite element method of analysis as an alternative design tool which is adaptable to a wide range of situations. Finite element models are developed to investigate the influence of the plastic flow rule, wall friction and the soil type on the behaviour of a cantilever support system. Subsequently, the effect of wall stiffness, prop stiffness and the application of prop loads on the performance of a multiple level support system is examined. The results from these studies focus on wall displacements, lateral earth pressures, bending moments, plastic strain patterns and surface settlements behind the wall. The investigation provides extensive information about the entire soil-structure interaction of the system. This potential of the finite element method can be used in the optimization of support system design.
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    Investigation of stabilized Berea Red soil with emphasis on tensile and cyclic triaxial tests
    (1989) Clayton, Russell Adrian; Scheele, F
    This dissertation investigates the soil mechanical properties of a sample of Berea Red soil and the most suitable methods of treatment to improve it. Special attention has been paid to lime stabilization and different curing techniques. Gradings, special indicators and California Bearing Ratios were determined on both natural and lime stabilized Berea Red soil. Consolidometer tests were performed on natural and lime or cement stabilized soil at various densities to establish the compressibility and collapse potential. A computer controlled Indirect Tensile Testing with data logging facilities was developed in apparatus order that some of the soil mechanical properties of Berea Red soil may be determined. Natural and stabilized Berea Red soil was tested in a monotonic and cyclic triaxial apparatus to determine the short and long stress strain characteristics.