Thermally induced pore pressure response in peat beneath a railway embankment

Abstract

This paper presents the results of a study investigating the behavior of peat subgrade beneath a railway embankment. Instrumentation was installed to measure the temperature, pore water pressure, and vertical settlement at different depths within peat strata over a 3-year period. The pore pressures within the peat subgrade were observed to increase significantly during the warmer months (>10 kPa) and to be strongly correlated to the seasonal changes in temperature. However, no clear correlation was found between pore pressure and settlement. Gas bubbles observed coming up through ponded surface water beside the embankment suggested that pore pressure may be a result of the expansion of gas bubbles within the peat. To confirm this hypothesis, laboratory tests were conducted. Peat specimens, kept at room temperature and in an anaerobic environment, confirmed the potential to generate gas. Further, the pore pressures of peat specimens placed within a triaxial cell apparatus with a constant applied confining pressure showed a direct correlation to incremental increases in the temperature of the specimen. Measurements showed that a 30 kPa increase in pore pressure corresponded to a 10°C increase in temperature. The results of this investigation showed the existence of gas within a peat subgrade and its effect on the pore pressure within the peat.