Quantification of the Settlement of an Embankment Constructed on Peat due to the Expulsion of Gases
Publication: International Journal of Geomechanics
Volume 17, Issue 3
Abstract
The mechanisms that result in the settlement of structures constructed on peat foundations have been the subject of numerous investigations. A recent study of the behavior of the peat subgrade showed that gas bubbles within the peat strongly influence the pore pressure. The thermal expansion of these gas bubbles results in an increase in pore pressure during the warmer months. The gas bubbles remain trapped until the pore pressure is sufficient to push them through the pore constrictions and toward the drainage boundary. The expulsion of the gas bubbles is followed by a sharp drop in pore pressure and a rapid change in volume. This paper presents the analysis of field data conducted to quantify the impact of this mechanism on the settlement of an embankment constructed on a peat subgrade. Measured pore pressures and deformations in the field are analyzed to show the acceleration of vertical deformation during the pore pressure drops. An approach developed from laboratory isotropic consolidation testing results is presented to correlate the magnitude of the drop in pore pressure to the corresponding volumetric strain. This correlation is then extrapolated to estimate the settlement of peat subgrade corresponding to the expulsion of gases. The results suggest that approximately 15% of the annual vertical settlement of the embankment occurs due to the cyclic dissipation of gas bubbles from the peat subgrade.
Get full access to this article
View all available purchase options and get full access to this article.
Acknowledgment
The authors acknowledge the contribution of Canadian National Railways for providing both the project and funding. This research was made possible through the (Canadian) Railway Ground Hazard Research Program and the Canadian Rail Research Laboratory, both of which are funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Pacific Railway, Canada National Railway, and Transport Canada.
References
Acharya, M. P., Hendry, M. T., and Martin, C. D. (2015a). “Thermally induced pore pressure response in peat beneath a railway embankment.” Int. J. Geotech. Eng., 10(2), 145–154.
Acharya, M. P., Hendry, M. T., and Martin, C. D. (2015b). “Effect of gas bubbles on pore pressure response in peat beneath a railway embankment.” Can. Geotech. J., 53(5), 765–772.
ASTM. (2007). “Standard test methods for moisture, ash, and organic matter of peat and other organic soils.” D2974-07, West Conshohocken, PA.
ASTM. (2008). “Standard test method for laboratory determination of the fiber content of peat samples by dry mass.” D1997-91, West Conshohocken, PA.
Barden, L. (1974). “Consolidation of clays compacted dry and wet of optimum water content.” Géotechnique, 24(4), 605–625.
Conte, E. (2004). “Consolidation analysis for unsaturated soils.” Can. Geotech. J., 41(4), 599–612.
Environment and Natural Resources of Canada. (2016). “Climate data 2011 to 2014.” ⟨http://climate.weather.gc.ca⟩ (Feb. 2, 2016).
Fredlund, D. G., and Rahardjo, H. (1993). Soil mechanics for unsaturated soils, Wiley, New York, 419–439.
Hobbs, N. B. (1986). “Mire morphology and the properties and behaviour of some British and foreign peats.” Q. J. Eng. Geol. Hydrogeol., 19(1), 7–80.
Konrad, J., Grenier, S., and Garnier, P. (2007). “Influence of repeated heavy ale loading on peat bearing capacity.” Proc., Canadian Geotechnical Conf., Ottawa Geo 2007, Canadian Geotechnical Society, British Columbia, Canada, 1551–1558.
Landva, A. O., and La Rochelle, P. (1983). “Compressibility and shear characteristics of Radforth peats.” STP 820, ASTM, West Conshohocken, 157–191.
Long, M., and Boylan, N. (2013). “Predictions of settlement in peat soils.” Q. J. Eng. Geol. Hydrogeol., 46(3), 303–322.
MacFarlane, I. C. (1965). The consolidation of peat: A literature review, National Research Council of Canada Division of Building Research, Ottawa, 8–393.
MacFarlane, I. C., ed. (1969). Engineering characteristics of peat, muskeg engineering handbook, University of Toronto Press, Toronto, 78–126.
Nageswaran, S. (1983). “Effect of gas bubbles on the seabed behaviour.” Ph.D. thesis, Oxford Univ., Oxford, U.K.
O’Kelly, B. C., and Zhang, L. (2013). “Consolidated-drained triaxial testing of peat.” Geotech. Test. J., 36(3), 310–321.
Qin, A. F., Sun, D. A., and Tan, Y. W. (2010). “Analytical solution to one dimensional consolidation in unsaturated soils under loading varying exponentially with time.” Comput. Geotech., 37(1–2), 233–238.
Sills, G. C., Wheeler, S. J., Thomas, S. D., and Gardner, T. N. (1991). “Behaviour of offshore soils containing gas bubbles.” Géotechnique, 41(2), 227–241.
Thomas, S. D. (1987). “The consolidation behaviour of gassy soil.” Ph.D. thesis, Oxford Univ., Oxford, U.K.
Weber, W. G. (1969). “Performance of embankments constructed over peat.” J. Soil Mech. Found. Div., 95(1), 53–76.
Zhou, W., and Zhao, L. (2014). “One-dimensional consolidation of unsaturated soil subjected to time-dependent loading with various initial and boundary conditions.” Int. J. Geomech., 291–301.
Information & Authors
Information
Published In
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Oct 12, 2015
Accepted: Jun 24, 2016
Published online: Aug 30, 2016
Discussion open until: Jan 30, 2017
Published in print: Mar 1, 2017
Authors
Metrics & Citations
Metrics
Citations
Download citation
If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download.