in : Projects
Kontur’s geotechnical assessment included seismic characterization of the site, subgrade and foundation design input for precast concrete headwalls and culvert pipe, steady-state seepage analysis, subgrade and foundation preparation, temporary excavation and unwatering, culvert backfill and dike reinstatement, bulk dike fill, riprap filter layer and annular drainage fill for the new culvert.
Kontur’s geotechnical assessment included seismic characterization of the site, subgrade and foundation design input for precast concrete headwalls and culvert pipe, steady-state seepage analysis, subgrade and foundation preparation, temporary excavation and unwatering, culvert backfill and dike reinstatement, bulk dike fill, riprap filter layer and annular drainage fill for the new culvert. Kontur conducted field reviews during construction and materials testing on the various fill materials for acceptance.
The 3.5 km long North Nicomen Dike, situated at the west end of Joe’s Slough, about 2.2km southwest of the community of Deroche, BC, was originally constructed in 1948 under emergency conditions in response to the flooding event on the Fraser River to provide partial protection for the low-lying areas north of Nicomen Slough. As a result, the dike was constructed of non-standard, locally sourced materials, including organics, silt, sand, and clay that would not meet current dike design standards.
Nicomen Slough flows parallel to the south side of the dike, and Joe’s Slough flows perpendicular to the north side of the dike at chainage 2+469. The project involves the reinstatement of the dike as a result of an old culvert with a broken floodgate and the desire to restore watershed connections. The project involves the replacement of the existing 700mm dia. CSP culvert with a 1200mm dia. concrete culvert complete with precast concrete headwalls at both the inlet and outlet ends. The new outlet end will be equipped with a self-actuating tide gate with an invert at about elevation 2.9m, geodetic, and rip rap erosion protection. The inlet end will feature soil wraps and erosion control around the headwall with an invert at about elevation 3.3m, geodetic. The project also included the construction of a 4m wide temporary access road on the land side of the dike to tie into the existing access road on either side of Joe’s Slough.
The project faced several challenges that were overcome through collaborative efforts between KWL, Kontur, the Contractor and their Consultant. Time constraints presented a challenge for this project with only four (4) months between the testhole exploration and completion of construction. Wet weather and the onset of the spring freshet also presented a challenge in terms of rising water levels in both Nicomen Slough and Joe’s Slough. The existing dike was constructed of silt that experienced localized stability issues with dike slope at the work site when the Contractor elected to use a vibratory hammer to install steel sheet-piles to construct a cofferdam on the Nicomen Slough side of the floodbox culvert. The soft subsurface conditions at the bottom of Nicomen Slough together with challenges dewatering the inside of the cofferdam necessitated changing foundation support for the headwall on the Nicomen Slough side to piles. Collaborative efforts between the Contractor’s Structural Engineer and Kontur allowed for installation of appropriate piles with only limited delay to the project.
