ZB
Z. Bitar
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1
Deep Sea Mining: An Adhesion Problem
A Study on Clay Adhesion
The clay adhesion phenomenon has been problematic in multiple engineering projects involving soft cohesive soils. In this dissertation, the adhesive characteristics of offshore high plasticity clay will be analyzed in support to deep sea mining applications. Adhesion of clays are particularly relevant in 2:1 swelling clays, where the magnitude of the force is highly dependant on the clay properties itself, working conditions and the soil engaging component surface material. The most prevalent force in offshore saturated conditions arises from the suction forces between micro-channels in the clay and the soil engaging component. Methods to reduce this adhesive force were assessed, ranging from solutions such as vibrations and electro-osmosis, to modifying the soil engaging surface to break continuous contacts between the clay and component. The natural adhesion of two typical offshore clays were experimentally determined by interface shear tests for the shear adhesion and pull-out tests for tensile adhesion. Interfacial shear strength was measured for typical materials found in the offshore industry, that being steel, aluminium, rubber and a polymer coating. Results from the tests showed that materials do have an impact on adhesive stresses. Similarly, pull-out tests showed this variation pattern. The influence of pull-out rates and contact time on adhesive tensile strength were also assessed and showed to increase with faster rates and longer contact times, respectively. In application to a typical rotational cutterwheel in deep sea mining, a scaled test-setup of a rack of cutter-teeth was dragged through the test clay to acquire horizontal cutting forces with the utilization of the experimentally found natural adhesion in the interface tests. The found adhesion value for the test clays were utilized to validate the cutting clay model from "The Delft Sand, Clay & Rock Cutting Model" (Miedema, 2019). Practical results from the scaled experiment seemed to coincide relatively well with the theoretical model. It is therefore recommended to further investigate the use of experimental means to determine adhesion of clays to develop an even more accurate empirical model.
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The clay adhesion phenomenon has been problematic in multiple engineering projects involving soft cohesive soils. In this dissertation, the adhesive characteristics of offshore high plasticity clay will be analyzed in support to deep sea mining applications. Adhesion of clays are particularly relevant in 2:1 swelling clays, where the magnitude of the force is highly dependant on the clay properties itself, working conditions and the soil engaging component surface material. The most prevalent force in offshore saturated conditions arises from the suction forces between micro-channels in the clay and the soil engaging component. Methods to reduce this adhesive force were assessed, ranging from solutions such as vibrations and electro-osmosis, to modifying the soil engaging surface to break continuous contacts between the clay and component. The natural adhesion of two typical offshore clays were experimentally determined by interface shear tests for the shear adhesion and pull-out tests for tensile adhesion. Interfacial shear strength was measured for typical materials found in the offshore industry, that being steel, aluminium, rubber and a polymer coating. Results from the tests showed that materials do have an impact on adhesive stresses. Similarly, pull-out tests showed this variation pattern. The influence of pull-out rates and contact time on adhesive tensile strength were also assessed and showed to increase with faster rates and longer contact times, respectively. In application to a typical rotational cutterwheel in deep sea mining, a scaled test-setup of a rack of cutter-teeth was dragged through the test clay to acquire horizontal cutting forces with the utilization of the experimentally found natural adhesion in the interface tests. The found adhesion value for the test clays were utilized to validate the cutting clay model from "The Delft Sand, Clay & Rock Cutting Model" (Miedema, 2019). Practical results from the scaled experiment seemed to coincide relatively well with the theoretical model. It is therefore recommended to further investigate the use of experimental means to determine adhesion of clays to develop an even more accurate empirical model.
Statistical Analysis of Geotechnical Parameters in Starnmeer and Alkmaardermeer
Dike Stability analysis
The aim of this thesis report is to analyze slope stability parameters given by HHNK for the dike around a polder located in the province of North-Holland, “Starnmeer”, and a lake located to the west of it called “Alkmaardermeer”. Most of the dike has been reported to be too low in some places and plans of restoration will be implemented in 2019. A RFEM (Random Finite Elemental Method) analysis is to be done in collaboration with TU Delft and HHNK on these dikes to identify slope failure probabilities, where the input data is to be addressed in this report. Starnmeer contains thick layers of peat and clay until a depth of approximately -5 meters NAP, where a large sand aquifer begins to much larger depths. For geotechnical analysis, the first few meters are of primary concern, so only the thick peat and clay layers will be assessed. Rising water levels proves problematic for the polder, but fortunately drainage opportunities to adjacent water bodies is possible. The addition or reduction of water heavily influences soil behavior by affecting underlying pore water pressures and stress states. Parameters to be analyzed include wet bulk density, dry bulk density, water content, cohesion, and the friction angle. A statistical analysis and distribution of each parameter provide meaningful insight on probabilities and disseminations of measurement data. The clay layer was found to have a significant amount of sand and silt, affecting the porosity, sorting, cohesion, and bulk densities resulting in an uncompacted porous clay layer. The peat layer is also highly saturated, highly organic, and rather loose. The layers are hence prone to heaving and rapid primary consolidation. By classifying each of the five parameters for both regions to be normally distributed or lognormally distributed, the data can be then standardized and correlated to each other to determine linear dependencies. The relations heavily vary depending on the environmental setting and other physical aspects. For instance, the wet and dry bulk densities are found to have a strong positive correlation with each other in Starnmeer but not in Alkmaardermeer. The layers were found to be heavily saturated, which negatively influences the correlation between water content and bulk densities. Cohesion and friction angle are primarily dependent on the consistency, shape, and packing of the soil grains, so low to no correlation was established.
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The aim of this thesis report is to analyze slope stability parameters given by HHNK for the dike around a polder located in the province of North-Holland, “Starnmeer”, and a lake located to the west of it called “Alkmaardermeer”. Most of the dike has been reported to be too low in some places and plans of restoration will be implemented in 2019. A RFEM (Random Finite Elemental Method) analysis is to be done in collaboration with TU Delft and HHNK on these dikes to identify slope failure probabilities, where the input data is to be addressed in this report. Starnmeer contains thick layers of peat and clay until a depth of approximately -5 meters NAP, where a large sand aquifer begins to much larger depths. For geotechnical analysis, the first few meters are of primary concern, so only the thick peat and clay layers will be assessed. Rising water levels proves problematic for the polder, but fortunately drainage opportunities to adjacent water bodies is possible. The addition or reduction of water heavily influences soil behavior by affecting underlying pore water pressures and stress states. Parameters to be analyzed include wet bulk density, dry bulk density, water content, cohesion, and the friction angle. A statistical analysis and distribution of each parameter provide meaningful insight on probabilities and disseminations of measurement data. The clay layer was found to have a significant amount of sand and silt, affecting the porosity, sorting, cohesion, and bulk densities resulting in an uncompacted porous clay layer. The peat layer is also highly saturated, highly organic, and rather loose. The layers are hence prone to heaving and rapid primary consolidation. By classifying each of the five parameters for both regions to be normally distributed or lognormally distributed, the data can be then standardized and correlated to each other to determine linear dependencies. The relations heavily vary depending on the environmental setting and other physical aspects. For instance, the wet and dry bulk densities are found to have a strong positive correlation with each other in Starnmeer but not in Alkmaardermeer. The layers were found to be heavily saturated, which negatively influences the correlation between water content and bulk densities. Cohesion and friction angle are primarily dependent on the consistency, shape, and packing of the soil grains, so low to no correlation was established.