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Trinity Railway Express Crossing Trinity River
Trinity Railway Express (TRE) offers premier commuter rail service between Fort Worth and Dallas. The existing section between I-35W and Sylvania Avenue in Fort Worth has been a single-track section, which crosses the Trinity River on a narrow 764-foot-long bridge that was constructed in 1903. This section is used not only by TRE commuter trains, but also Amtrak, Union Pacific, and BNSF freight trains. The age of the bridge, and the standards by which it was designed and constructed, require frequent inspection, monitoring, and maintenance to keep the bridge in service. Additionally, the bridge necessitates reduced speeds and stops for freight trains, causing delays to passenger trains. To resolve the issues, TRE needed to rehabilitate the existing historic Trinity River Bridge and add a second track.
The new bridge had was located very close to the existing bridge. A complication was that no drawings survived of the existing bridge foundations. Our challenge was to determine a suitable foundation that could be constructed within the right-of-way and adjacent to the existing bridge piers without interference from existing foundations. Also, the choice of retaining wall system was a challenge due to right-of-way limitations.
Continuous heavy rain events impacted the retaining wall subgrade soils, making maintaining the construction schedule a unique challenge during construction.
Provide geotechnical design and construction solutions to be able to build the track within limited Right-of-Way and schedule constraints.
HVJ conducted a geophysical study to identify the limits of the existing foundation and mapped it in a 3-D model. The clearance distance and the penetration depth was determined of the new 10-foot diameter mono-shafts so as not to impact the existing foundations during construction. Also, since the mono-shafts are offshore in the river, the design team required the use of casing and thermal integrity testing to ensure the integrity of the drilled shafts.
HVJ also worked closely with the design team and determined T-Walls were appropriate retaining wall structures within the limited Right-of-Way. Since the project involved double tracks, HVJ performed global stability and external stability analyses considering multiple loading scenarios with and without train loads on single and double tracks. Track location in relation to the wall face was very critical as it helped with stability analysis in some cases, and it reduced stability in others. HVJ conducted multiple iterations to determine the required wall stem length to meet stability requirements.
During construction, continuous heavy rain events impacted the wall subgrade soils. Additionally, since the track was "live," and we had a limited ability to shut down the track, we worked with DGR and White Hawk Engineering to create a solution for the wall without interrupting service. The solution included removing and replacing subgrade soils with a flexible base reinforced with geogrids, and using staged construction to finish building the wall to its full height to keep the project on schedule.
"HVJ provided the technology and knowledge to determine the extent and condition of the foundation below the surface, which provided the confidence in locating and constructing the second bridge as close as possible to the existing. HVJ was prompt in its investigation of the site. After heavy rains deluged the area, they were able to determine a solution that provided the soil stabilization required using resources readily available. A win-win for the project and project team!"