The Northstar Commuter Rail provides passenger service between Big Lake and Minneapolis, and connects to the Hiawatha Light Rail system that travels between the Mall of America and downtown Minneapolis. We were retained to provide quality assurance testing and special inspections for the Big Lake maintenance facility and six stations: Big Lake, Elk River, Anoka, Coon Rapids, Fridley and Minneapolis. In addition, we also provided geotechnical engineering and construction materials testing for the expansion of a BNSF third line to add capacity for commuter trains.
During construction of the stations and maintenance facility, we performed excavation observations during mass grading to evaluate the soil suitability for pavement and building support, and also performed numerous compaction tests to determine that the densities obtained in the field met the Minnesota Department of Transportation (MnDOT) project specifications. Our quality assurance testing included soils, concrete, rebar and masonry, and our special inspections included concrete reinforcement, concrete testing, masonry observations and structural steel. Testing was performed on both inbound and outbound station platforms, overhead walkway bridges, tunnel entrances and exits and parking lots. Challenges included encountering soft soils with the Minneapolis station. We subcut the soft clays to a depth of approximately 10 feet and backfilled with sand, which provided structural support and helped prevent frost heave issues.
