Slope failures in infrastructure assets across the UK and Ireland have been observed in recent years. These failures can in many cases be attributed to progressive failure. The mechanisms which cause progressive failure are not understood and research is ongoing in many areas to understand them. One process under investigation is strength reduction by strain softening due to seasonal cycles in pore water pressure. The research presented here has incorporated field investigations, laboratory testing and numerical analysis to assess the geomechanical response of glacial till cuttings to climatically driven pore water pressure cycles. Three research sites were selected and their geotechnical and hydrogeological properties characterised through field investigation and laboratory testing. Alternative methods of in situ stiffness measurement have been used to establish the small strain stiffness to the formation for use in numerical simulations. A pore water pressure monitoring programme has been established across three study sites and provides a comprehensive dataset for use in this and future analyses. Pore water pressures are seen to be driven by climate controlled recharge. Advanced stress path testing was carried out in the laboratory to assess the possibility of strain softening. Reconstituted samples of glacial till were taken through extension and compression loading, followed by controlled pore water pressure cycles to simulate seasonal changes. From these tests shear strain was observed to continue with no increase in deviator load, indicating that strain softening maybe possible in this soil deposit. Validated numerical models of coupled stress-strain and pore water pressure have been compiled which represent the overconsolidated glacial till cuttings in this area. From this base climatically driven pore water pressure cycles were simulated. Shear strains are recorded as increasing with time with the greatest magnitude of change occurring at the toe of excavations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:669676 |
| Date | January 2014 |
| Creators | Carse, Laura Ann |
| Publisher | Queen's University Belfast |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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