As the Bridge Task Leader, T. Y. Lin International designed the majority of the structures for two new extensions of San Diego’s Light Rail Transit (LRT) system though the Mission Valley area of San Diego. The combined length of the two double-tracked extensions was 12 miles, of which approximately five miles ran on various elevated guideways, ranging in length up to one mile each. In total, T.Y. Lin International was involved in the preliminary engineering, final design, and/or oversight of 16 bridges and four aerial stations(including construction support) in partnership with Parsons Transportation Group for the Mission Valley East LRT Extension project and Boyle Engineering Corporation (now AECOM) for the Mission Valley West LRT Extension project.
- 12 miles of new, double-tracked LRT
- Bridge task leader for 16 bridges and two aerial stations
- Four major river crossings and two aerial freeway crossings
- Significant seismic challenges, including lateral spreading and liquefaction
- Multiple awards
In addition to developing the bridge design criteria and preliminary engineering and alternative analysis during the environmental clearance process, engineers also conducted type selection and value engineering analysis. The team went on to prepare the construction drawings and specifications for ten bridge structures, including four crossings of the San Diego River and two aerial freeway crossings.
One of the biggest challenges of these projects was the geological setting and seismicity of the location. Subsurface soils consist of man-made fill, alluvium, bay deposits, and consolidated clay. The Rose Canyon Fault zone located at the westerly end of Mission Valley is classified as a major zone of active right-lateral faulting and is recognized to produce large earthquakes.
Making use of T.Y. Lin International’s considerable seismic design experience, engineers implemented state-of-the-art technical solutions with considerations for lateral spreading of the San Diego River embankments. The site was also classified as susceptible to seismically induced liquefaction. To mitigate this potential hazard, ground improvement measures such as installation of stone columns and/or compaction grouting of the soil in the area around the cast-in-drilled-hole concrete piles were implemented. All of this was done while minimizing impacts to sensitive environmental areas, especially the San Diego River.
The two projects received multiple awards, including two Bridge Structures Awards from the American Concrete Institute (ACI), the American Society of Civil Engineers (ASCE) Project of the Year, and American Society of Civil Engineers (ASCE) Award of Excellence.