'Large cut slopes (excavations) in glacial tillare a common occurrence along road and rail networks in Northern Ireland, due to unique drumlin topography in the province. Despite observed occurrences of delayed slope failures within till cuttings, their long-term performance is not well understood. Decreases in the stability of overconsolidated clay till slopes with time have been shown to be in response to pore water pressure (PWP) cycles induced by soil-climate interactions. This research has developed and presented an understanding of the mechanisms controlling PWP fluctuations within till slopes in response to climatic factors. Three cut slopes in till were instrumented to measure PWP variations, surface soil water content, suction, and shallow water table fluctuations. Field and laboratory tests were carried out to characterise the geotechnical and hydraulic properties of the till. The field instrumentation facilitated the identification of a number of characteristic controls on PWP variations, including the seasonal soil water balance and more rapid PWP responses due to gravity driven recharge and stress changes. A numerical soil water storage model was used to estimate the temporal variability in recharge to the till. This water balance accounts for PWP variation, in-situ hydraulic conductivity and fracture porosity within the till. The outputs from the water balance model were subsequently used as a boundary condition in a transient seepage model. This is coupled with a limit equilibrium analyses to assess variability in the factor of safety of the cuttings. Furthermore, a generic model was used to explore how variations in climatic and hydrogeologic conditions will affect long-term slope stability. The research highlights the control of the hydrogeologic setting and climatic conditions on PWP dynamics, and makes suggestions for how this understanding can be used in design, management and remediation measures of cut slopes to protect these assets in the future.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:679266 |
| Date | January 2014 |
| Creators | McLernon, M. |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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