Crowder Construction Company asked KCI to provide a value engineering study to evaluate constructability issues associated with the Norfolk Southern Railroad crossing over Coddle Creek in Cabarrus County, North Carolina. The new bridge is part of a 15-mile stretch of new rail track carrying high speed railroad traffic between Charlotte and Raleigh.
The proposed 160-foot-long, three-span structure was located adjacent to an existing railroad bridge that was built in the early 1900s and had to remain in service. After the project was awarded to Crowder and track construction had begun, it became apparent that the proposed high-wall abutment foundations would be in direct conflict with the existing bridge foundations, making it virtually impossible to construct.
Our team of structural engineers assisted Crowder in evaluating their options by performing alternative preliminary designs and analyses. They determined that the bridge could be lengthened in order to avoid conflicts with the existing foundations. One constraint to the revised bridge design was that the structural steel beams had already been ordered and fabricated. KCI recommended that the Span A beams be relocated to Span C. Consequently, the Span C beams could be moved to Span A with an additional 25 feet of beam length spliced on. As a result, the high-wall abutments from the original design were eliminated and replaced with constructible abutment caps, which would be supported by drilled shaft foundations.
An independent soldier pile retaining wall was designed to be in front of Abutment 1 to limit the impact of fill slope on the already completed hydraulic model and environmental permits. The soldier pile wall saved Crowder from having the hydraulic model and environmental permits renewed, which can be a prolonged process.
The proposed horizontal alignment directly adjacent to the existing structure caused additional constructability concerns, including the shoring needed to install the new abutments. The in-service mainline track has a relatively high volume of train traffic (approximately 30 trains per day). This created additional constructability concerns. Due to the reduced abutment height of KCI’s revised design, the required shoring height went from approximately 30 feet to nine feet. The new shoring wall would be within 11 feet of the live mainline track and needed to be designed to withstand the Cooper E80 surcharge load, as well as limit deflection of the wall to 3/8 of an inch as required by Norfolk Southern. KCI had multiple meetings with Crowder, the NCDOT Rail Division, and Norfolk Southern to discuss options for acceptable design of this shoring. Our team’s solution was a secant pile wall as a permanent shoring/retaining wall between the structures. Given the large capacity and moment of inertia this type of wall possesses, engineers felt this was the best alternative to resist deflection from the large surcharge from the active train line. NCDOT and Norfolk Southern agreed with the idea and iterated with KCI on the final design. Additionally, NCDOT required KCI to produce a special provision for construction of the secant pile wall. This was the first permanent secant pile wall constructed on a NCDOT funded project. It was also the first permanent secant pile wall constructed adjacent to Norfolk Southern live tracks.
Because this bridge was on the critical path and already behind schedule, our team worked nights and weekends in order to submit revised structure plans and design calculations within an expedited time frame.
R. Eric Burgess, PEPractice Leader
When KCI was originally approached for design on this project, it was behind schedule due to the fact that the bridge was not constructible. Our team worked nights and weekends in order to submit revised structure plans and design calculations within that time frame. Once the plans were submitted, KCI participated in bi-weekly conference calls to address comments and make the necessary changes requested by Crowder, NCDOT, and Norfolk Southern. Several revisions were made, including the design plans and special provisions, and resubmitted to the NCDOT ahead of schedule. In the end, KCI exceeded the expectations of the client by providing a constructible bridge design on an accelerated design schedule. KCI’s ISO policy was utilized in order to ensure that quality controlled calculations and plans were delivered within the accelerated schedule. As a result of KCI’s good standing relationship with Crowder, a separate project number was created to handle the contractor services design out of KCI’s Charlotte office. This is included a work bridge over Coddle Creek to allow cranes to install the required drilled shafts.