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.

This paper presents the pore pressure behaviour observed within peat beneath a newly constructed railway embankment. Piezometers installed at different depths beneath the structure showed episodic increases in pore pressure above hydrostatic pressure followed by a rapid pore pressure decrease. It was postulated that this fluctuation in pore pressure was due to the movement and expulsion of gases within the peat. Investigations were conducted in the laboratory to replicate this pore pressure response. The peat specimens were subjected to isotropic consolidation, within a triaxial cell, at constant confining pressure while measuring the change in the specimen’s pore pressure and volume. The results of this investigation indicate that the gas bubbles move through the channeled network of voids towards the drainage boundary where they restrict the flow of water, which results in the increase of pore pressure towards an upper limit or escape pressure, ultimately causing an expulsion of gas bubbles. This expulsion of bubbles results in a rapid drop in pore pressure and volume change within the specimen. The implications of the volume change associated with this pore pressure behaviour are discussed.

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