Oil sands tailings are a warm aqueous suspension of sand, silt, clay, residual bitumen and naphtha. The tailings are hydraulically transported and stored in tailing ponds where they segregate, with the sand settling from suspension forming beaches and the remaining tailings flowing to the middle of the pond. After several years of tailings disposal, three layers have developed in the pond, which are, from top to bottom, water, thin fine tailing and mature fine tailing (MFT). MFT is the major reason that the tailing ponds cannot be reclaimed. Due to low the high water content and low hydraulic conductivity, MFT consolidate very slowly in the ponds. Therefore, many technologies have been proposed remove the water from the tailings and increase the consistency so that the tailing pond can be reclaimed. but most of these dewatering technologies are rejected due to the limited technical or economic feasibility. In this PhD thesis, two potential fine tailings management technologies were described. These two technologies were: (1) sub-aerial drying of fine tailings deposited in thin lifts, and (2) use of prefabricated vertical drains (PVD) in enhancement of consolidation of fine tailings in the pond. In this PhD project, experiments were carried out to investigate geotechnical properties and dewatering behaviour of fine oil sands tailings related to the described technologies.@en

This book presents the proceedings of the 21st European Young Geotechnical Engineers Conference (EYGEC), held in the Netherlands in September 2011. Six sections cover the topics of: underground construction; pile foundation and ground improvement; soil dynamics; dams, erosion and piping; deformation and soil properties and geothermics. The papers included here present the new and refreshing perspective of young engineers exploring the field of geotechnics.@en

This book presents the proceedings of the 21st European Young Geotechnical Engineers Conference (EYGEC), held in the Netherlands in September 2011. Six sections cover the topics of: underground construction; pile foundation and ground improvement; soil dynamics; dams, erosion and piping; deformation and soil properties and geothermics. The papers included here present the new and refreshing perspective of young engineers exploring the field of geotechnics.@en

This thesis entitled “Compaction of Silty Sands through Biogenic Gas Desaturation Pretreatment” investigates a method to improve compactibility of an initially fully saturated soil body bringing it to a saturation corresponding to the optimum water content of the targeted soil layer. The process comprises two stages: a reaction phase to desaturate the soil body, and compaction phase where the necessary loading is applied to the system. The substrate solution with predetermined concentration, combined with a bacterial inoculum to convert the substrate into nitrogen gas, is injected into the soil and left to react. Gas is produced in-situ as a result of the stimulation of the bacteria which creates a local overpressure and expels water from the system. The desaturated soil body is subsequently compacted. The aim is to achieve a higher degree of compaction with the same energy, or the same degree of compaction with less energy input in the desaturated soil as opposed to the fully saturated case where energy is wasted on expelling water.

Organic soils and peat soils are widely distributed across the world, particularly in the Northern hemisphere in countries like Canada and Russia having 170 and 150 million hectares respectively and in tropical regions such as Indonesia and Malaysia, which contain 26 million and 3 million hectares respectively. Organic soils and peat are considered problematic materials for construction. Due to their high water content and high compressibility, they are unsuitable material to support any foundation and other type of loading in their natural state. However, as population grows every year, land becomes scarce and the need to use this land for agriculture or construction is rising. In practice, these waterlogged soils are drained before any potential usage for construction. However, drainage requires significant time and leads to settlements or subsidence. Subsidence in organic soilsmay cause damage or high maintenance costs to buildings and infrastructure or require significant amount of materials to raise or maintain surface level, which may be costly or have significant environmental impact. Subsidence of peat also occurs in rural areas. Peat meadows are drained through networks of ditches and waterways to enable farming or agriculture. These waterways require regular dredging to keep them open from plant growth and prevent them to fil up with partly degraded organic matter. In this project ‘Lift up Lowlands’ the potential of using these dredged organic sediments to compensate surface subsidence in peatlands is investigated… @en

Waterways and lakes in low-lying delta areas require regular dredging for maintenance. Reuse of dredged sediments has been proposed for various applications. However, directly after dredging the physical characteristics of these sediments make them generally unsuited for immediate reuse. They are often placed on land, where they are allowed to ripen through a combination of drainage, consolidation and evaporation. At a certain stage during the desiccation process cracks will develop, affecting the physical properties of the material. These include its strength, stiffness and hydraulic conductivity, as well as drainage, water infiltration and evaporation. The soil composition can be likewise altered by biochemical processes, which are stimulated by the ingress of oxygen through the cracked surface. Consequently, identifying how cracks develop in the soil is essential for understanding the behavior of the material. Much investigation has been performed studying desiccation cracks, but the underlying mechanisms are still not fully understood. It is known that the drying speed affects the final amount of cracks in a soil, which points out to the potential impact of rate effects in soil cracking. The effects of the drying rate might be related to variations in the tensile strength influenced by different shrinkage rates, as well as its impact on the suction development in the soil. In this thesis different sets of experiments were carried out to study the phenomenon of desiccation fracturing in soil. The first series of tests were carried out in a controlled laboratory environment to study the crack development in drying clay slurries under different initial and boundary conditions. The outcomes of those tests indicated that cracks can propagate in a different way than commonly assumed (namely under the surface) and that fracture characteristics strongly depend on the initial and boundary conditions. A second series of tests examined the combined effects of pull rates and high water contents on the tensile strength. Particle Image Velocimetry analysis was also carried out on pictures taken during the tests to examine the strains generated. It was found that the effect of pull rate on the tensile strength of the clay was negligible compared to the effect of the water content. Pull rate did affect the stiffness response of the soil. The findings revealed that the influence of the evaporation rate on soil fracturing might be related more to the rate dependency of the stiffness rather than to significant changes in tensile strength. The last series of experiments investigated the drying behaviour of a clay with different initial water contents and under different evaporative conditions. The small scale evaporation experiments carried out using commercially available suction measuring equipment with an adjusted test procedure. The results showed that the initial conditions have great influence on the drying performance of a soil, which can be partly attributed to the influence of the surface texture and the pore structure. It was observed that under certain circumstances, the evaporation of a soil surface can be higher than that of open water. The different evaporation rates had a marked effect on the water distributions with depth within the soil. The evaporation rate also produced a dynamic response of the soil water retention curve. At the end, a simple one-dimensional model was set up to try to capture the behavior observed during all the laboratory tests. It also served to analyze the consequences of different hypotheses about the material behaviour on the crack onset in a homogenous soil layer undergoing surface drying. @en