39400m Horizontal Placement of Wick Drains
Minette Substation project was part of the expansion of the existing substation located in Kitimat, BC. Menard was awarded the site preparation package for the expansion of the substation.
The site’s general subsurface stratigraphy consisted of the following:
• Fibrous and highly compressible peat layer to a depth of 2m with almost 100% moisture content;
• Underlaying sand and gravel to a depth of 3m;
• Underlaying interlayered, very soft clayey silt to a max. depth of 13m;
• A layer of fine sand overlying a strong bedrock at approx. 25m depth.
Menard Canada Solution
The subsurface profile of the substation required the placement of the preload material to initiate consolidation and reduce the future settlement of the structure. Wick Drains and horizontal drains tend to accelerate the surcharge fill loading time. Menard, a pioneer in the Wick Drains industry of Canada, installed the vertical drains to a maximum depth of 25m below the grade level to the bedrock in addition to horizontal drains. These drains also act as an excellent passage for the dissipation of the pore water pressure during a seismic event.
The fill material, consisting of sand and gravel material, along with the presence of cobbles, placed below the working platform affected the productivity of the Wick drain installation. The points were predrilled to avoid damage to the mandrel and potential refusals due to the presence of cobbles.