Construction of Road Embankment over Priddis Slough Using Wick Drains and Preloading

ABSTRACT: To accommodate the continuing growth in the West Macleod area in South Calgary, a new roadway consisting of an approximately 10 m high embankment, known as 194th Avenue S.E. Priddis Slough Crossing, was constructed over an environmentally sensitive low-lying area within a large body of water. The subsurface conditions consist of soft and organic pond deposits over a highly variable sand and gravel layer, over clay deposits ranging from 10 m to 20 m in thickness, underlain by sedimentary bedrock. Area-wide preloading was required to construct the roadway which included constructing a single-span wildlife bridge founded on steel piles. The effects imposed by the on-going settlement was a consideration in the design of the bridge crossing and associated retaining structures. Calculated maximum settlement was in the order of 500 mm. Further, in order to meet the target schedule for road opening, construction of the roadway required installation of area-wide wick drains and preloading technique to accelerate consolidation settlement. This paper describes the geotechnical and instrumentation program completed during construction, reviews selection of the wick drain material, compares the estimated and measured embankment settlements, and discusses constructability issues during installation of gravel shear keys and wick drains through the surficial sand and gravel layer.