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Title: Impacts of climate and vegetation on railway embankment hydrology
Author: Briggs, Kevin M.
ISNI:       0000 0004 2715 1650
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2011
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Field observations and numerical analysis have shown that seasonal changes in pore water pressure affect the stability and shrink-swell behaviour of clay fill railway embankments. However, the soil-atmosphere processes affecting railway embankment hydrology and the worst case conditions for pore water pressure variation are not well understood. This thesis explores the impact of climate and vegetation on pore water pressures within railway earthworks. Monitoring data from two instrumented embankments and piezometer data collected across the London Underground Ltd network were examined and compared with a hydrological finite element model incorporating a climate boundary condition. Monitoring and finite element modelling of an instrumented embankment in Kent showed that seasonal pore water variation is dependent on seasonal weather extremes, slope vegetation cover and the saturated permeability of the clay fill. Examination of London Underground Ltd monitoring data showed that foundation geology influenced maximum pore water pressure measured during an extremely wet winter, with a clear distinction between London clay founded and chalk or terrace gravel founded embankments. A numerical model confirmed that during extreme winter weather maximum pore water pressures are higher in clay fill embankments founded on clay than embankments underdrained by a more permeable foundation. Monitoring and finite element modelling of tree removal at an instrumented embankment in Essex showed that trees significantly influence pore water pressures, creating soil suctions at depth within their root zone. A finite element model of tree removal showed rewetting and a loss of soil suction within the embankment, in agreement with the monitoring data. The findings show that climate, vegetation cover and the saturated permeability of both the embankment fill and the foundation influence the extent of seasonal and maximum pore water pressures within railway embankments. This can be used by infrastructure owners during risk assessment of slope failure or poor performance of railway embankments.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available