Measurement of cyclic response of railway embankments and underlying soft peat foundations to heavy axle loads

Abstract

This paper presents the deformation and pore-water pressure response within peat foundations below three different railway embankments in response to cyclic heavy axle loading. The study sites include two at Canadian National (CN) Railway's Edson and Lac-La-Biche subdivisions in northern Alberta, and one at CN′s Lévis subdivision in southeastern Quebec. The three sites were instrumented to monitor the spatial distribution of strain, pore pressure generation, and stress, and the distribution of horizontal cyclic displacement with depth during the passage of trains. The horizontal cyclic displacement with depth was measured using a ShapeAccelArray (SAA). An analysis was conducted to determine how close the peat is to yielding under heavy axle loads. This analysis was based on the elastic response determined from undrained triaxial testing, a constitutive model developed for peat, and finite element modelling. The field response and the numerical modelling suggest that the embankments at the northern Alberta sites are stable under current loading conditions. The highest potential for yielding at these sites occurs just beneath the embankment and at the interface between the peat and underlying stiffer soil. At the Lévis site the analysis suggests that a recently constructed ditch concentrates shear stress at a location where the principal stress orientation corresponds to a reduced strength of peat and may have increased the potential for yielding.