BNSF Railway Co.’s bridge over the Coweeman River in Kelso, Washington, is shared by freight and commuter rail lines and runs along the Interstate 5 rail corridor. The 1908 Warren truss double-track structure was no longer able to accommodate the amount of rail traffic — it was part of a larger congestion issue that included a major bottleneck for trains traveling in and out of the Port of Longview. To reduce the congestion, a coordinated effort between the Washington State Department of Transportation and BNSF designed and constructed a new bridge that expands the rail capacity over the river.
The new 246-foot-long, single-track structure features a 164-foot through-plate girder main span and two double-voided box beam approach spans. Each pier was founded on a row of four 54-inch-diameter drilled shafts, which are permanently cased through surficial loose soil and were extended into the medium-dense sand using wet construction methods. The new bridge was part of a larger triple-track project that allows the traffic to be separated into freight and passenger lines.
Hanson supported BNSF in this project with civil/structural design, geotechnical investigation, environmental permitting and construction support services. Early in the project, several risks associated with the drilled shaft construction methods — including environmental concerns and that the casing installation’s vibrations could affect the Warren truss bridge — were identified and contingency plans were put in place prior to excavation. As part of our quality assurance measures, we provided full observation and documentation throughout the excavation and concrete placement.
But the work wasn’t done after the shafts were installed. Our team conducted a post-construction assessment using crosshole sonic logging and tomography. The interpretation of the initial post-construction assessments supported that four out of the eight drilled shafts could contain anomalies, such as an inclusion of sand or slurry in the concrete. In response, the contractor submitted a plan to core-drill, camera-inspect and remediate any flawed concrete through pressure grouting.
When the core samples were extracted, it was confirmed that there was a substantial anomaly near the tip elevation at one of the drilled shaft locations. To repair it, a pressurized tip grouting procedure was used: grout was injected under pressure through the core hole to improve the bearing conditions at the shaft tip by consolidating the disturbed material, strengthening the weak concrete and reestablishing the contact between the drilled shaft and suitable bearing soils to meet design specifications.
With effective planning and adaptability before and during construction and with a careful evaluation of the new structure, BNSF has a new bridge that helps improve rail service in the Pacific Northwest. Contact Matt Willey at firstname.lastname@example.org or Mike Buckley email@example.com to learn how our services can help with your next structural rail project.