Dahlie Road/CN Rail Overpass
Location: Smithers, British Columbia, Canada
Client: MMM Group / Ruskin Construction Ltd.
In 2008, MEG Consulting Limited (M+EG) was retained by MMM Group to provide geotechnical design services for the construction of a new overpass in Smithers, BC. The overpass spanning over the CN rail line was a design-build project contracted by Canadian National Railway. The overpass was constructed to provide 2-lane traffic on Dahlie Road, in order to eliminate the traffic congestion caused by the rail traffic. The design of the overpass consists of 2 mineral fill MSE embankments, a gas line protection slab and a 23-m long bridge structure. The estimated contract price is about 4.25 million dollars.
M+EG’s scope of work includes the following:
- Site investigation (test pit excavation and dynamic cone penetration test);
- Laboratory testing;
- Engineering analyses: bearing capacity under MSE reinforced zone, embankment stability, settlement assessment, seismic evaluation;
- Provide geotechnical input for the design of the gas line protection;
- Pavement design;
- Site inspection services to review the on-site compaction test program, the subgrade condition for the MSE wall, and the construction of the overpass.
- The settlement associated with the west embankment construction was considered critical for the existing utilities and the design of a protection slab. Settlement profiles were estimated considering the potential variations in soil conditions and compressibility along the alignment.
- During construction, the constructor encountered soft areas at subgrade level at the east embankment. The constructor was concerned about the presence of soft material that may have extended to several meters below the subgrade; the potential increase in construction cost would have been significant. M+EG visited the site to examine the soft materials and deemed that this was a result of the construction procedure being used. Simple remediation measures were provided.