Stabilization of Rail Track Bed Mile 9.0 – 9.1, CN, Dundas Subdivision

ABSTRACT: A single-track rail line was constructed at the study site in a 15 m deep cutting in the 1850’s, a second track was added to the north of the initial track in the 1890’s. The soil profile consists of a layer of low permeability sandy silt with a trace to some clay in the base of the rail cutting which extends to a depth of about 3 m below the base of rail, where it is underlain by a layer of sand. The phreatic pressure in the sand layer was up to about 4 m above the rail track. The sandy silt layer which lies at the base of the cutting has behaved as an aquitard confining the pressure in the underlying sand layer. Breakouts of pressurized groundwater have randomly occurred in the cutting base; upward seepage through the silt has resulted in erosion of “pipes” which in turn resulted in track instability. Such instability required the imposition of severe slow orders on train movements and a 24 hour-a-day watch. Track stabilization has been carried out in three phases over a period of 23 years. The first two phases were regarded as temporary and were intended to reduce the severity of slow orders until a permanent solution to the instability could be implemented. Both of the initial phases involved the removal of the then existing rail track and track bed, and construction of a new bed which incorporated a variety of geosynthetic reinforcing. The designs provided satisfactory support to carry a fully loaded train across a 0.5 m diameter void. The third phase of stabilization was designed to provide a long-term solution to the track instability by permanently reducing the phreatic pressure such that breakouts of groundwater would no longer occur. All of the applied corrective measures have been successful within their design expectations.