Soil suction is one of the most important physical variables affecting the soil engineering behavior, moisture content. Suction has a major controlling influence on soil shear strength. The moisture diffusivity properties of unsaturated properties of soils exert a critical influence on the depth to which seasonal variations of moisture and suction at the ground surface extend into the soil mass. Hence, a study of moisture diffusion coefficient is pivotal. In this research the drying test originally proposed by Mitchell (1979) has been validated by back calculating the moisture diffusion values using the empirical relation established by Lytton (2003). The non-linear flow through unsaturated soils has been simplified to a linear problem for simplicity in this study. Owing to this simplification, certain refinements have therefore been applied in the determination of diffusion coefficient. Thermocouple psychrometer was used to measure the soil suction along the length of the sample and at different times in the laboratory. Initial suction measurements were done using the filter paper test. Curve fitting procedure established by (Aubeny and Lytton, 2003), has been used for the determination of the diffusion coefficient. Analytical validation of the moisture diffusion coefficient, required coefficient of permeability, ??k??, slope of suction water characteristic curve ??S?? and air entry value ??ho?? as the major input parameters. Mitchell (1979) assumed the value of ??ho?? to be 100 cm. In this research air entry value, ??ho?? has been re-evaluated and it comes out to be higher than the pre estimated value. The value of slope of suction water characteristic curve, ??S?? obtained from pressure plate tests, compares well to the empirical equation of Lytton (2003). The results of moisture diffusion coefficient obtained from the empirical equation come out in the same range as obtained from the refined Mitchell??s (1979) drying test. The refinements includes introduction of constant temperature environment. Owing to the least variation in temperature, more reliable and reproducible data was obtained. The range of moisture diffusion coefficient, ??-values obtained from empirical equation, comes out to be coherent with the laboratory data. Hence, it can be concluded that the research was successful.

The disposal of fine-grained mining and industrial waste by formation of hydraulic-fill tailings dams is becoming a design and construction activity of increasing scale. In light of the increasing pressure on the mining industry to sustain stringent safety and environmental standards it is becoming more important to gain technical knowledge of the waste problem. The upper layers of the tailings residue dams are in the unsaturated state with the matric suction component contributing to the overall shear strength. The ability to incorporate the matric suction component in shear strength calculations is important to safe design. This research project investigates the use of the mid-plane suction probe to measure matric suction. The results obtained from the probe is used along with various tests to construct a complete soil-water characteristic curve for Mispah gold tailings as well as to investigate suction induced shear strength of drying tailings with depth. The tests were conducted on gold tailings from Vaal Operation’s Mispah tailings dam. The laboratory tests consisted of a trough test, to determine the soil-water characteristics of the gold tailing and also a drying box test that simulated the drying and desiccation of the gold tailings in the daywall. The project concluded that the mid-plane suction probe could be used with acceptable accuracy to determine soil suctions. The model for the prediction of the soil water characteristic curve, derived by Fredlund and Xing (1992), was used successfully to predict the complete soil water characteristics curve for Mispah gold tailings. The equation derived by Vanapalli et al. (1996) was successfully used to calculate both the normal and suction induced shear strength of gold mine tailings using either the volumetric water content from the extracted samples or from the soil water characteristic curve. / Dissertation (MEng (Geotechnical Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

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Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.

Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.

Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.

Gelfill (GF) is made of tailings, water, binder and chemical additives (Fillset, sodium silicate gel). The components of GF are combined and mixed on the surface and transported (by gravity and/or pumping) to the underground mine workings, where the GF can be used for both underground mine support and tailings storage. Thermal (T), hydraulic (H), and mechanical (M) properties are important performance criteria of GF. The understanding of these engineering properties and their evolution with time are still limited due to the fact that GF is a new cemented backfill material. In this thesis, the evolution of the thermal, hydraulic, mechanical, and microstructural properties of small GF samples are determined. Various binder contents of Portland cement type I (PCI) are used. The GF is cured for 3, 7, 28, 90, and 120 days. It is found that the thermal, hydraulic and mechanical properties are time-dependent or affected by the degree of binder hydration index. Furthermore, a relationship is found between the compressive strength and the saturated hydraulic conductivity of the GF samples. The unsaturated hydraulic properties of GF samples have also been investigated. The outcomes show that unsaturated hydraulic conductivity is influenced by the degree of binder hydration index and binder content, especially at low suction ranges. Simple functions are proposed to predict the evolution of air-entry values (AEVs), residual water content, and fitting parameters from the van Genuchten model with the degree of hydration index (α). Furthermore, two columns are built to simulate the coupled thermo-hydro-mechanical (THM) behaviour of GF under drained and undrained conditions. The obtained results from the GF columns are compared with the small samples. It is observed that the mechanical properties, hydraulic properties (suction and water content), and temperature development are strongly coupled. The magnitude of these THM coupling factors is affected by the size of the GF. The findings also show that the mechanical, hydraulic and thermal properties of the GF columns are different from samples cured in plastic moulds.