Tunneling to Connect Fort Worth

By David Wallace, P.E.

Along the south side of downtown Fort Worth, Texas sits Interstate 30, Tower 55 Rail Intersection—one of the nation’s busiest railroad intersections –and a newly revitalized urban, mixed-use neighborhood and medical district called the Near Southside. Originally, Interstate 30 ran elevated over a major east-west corridor on the south end of downtown but in the early 2000s, the highway was relocated further south to a more industrial area which include a highly active east-west railroad corridor. When the new highway was built, it flew over the railroad tracks leaving an underpass to be excavated in the future to connect a perpendicular street, Lamar (on the north) and Hemphill (on the south). Since then, the long-held desire of the City of Fort Worth to connect the central business district to the south side of town via an underpass tunnel that provides a safe, multi-modal route to and from downtown, gained momentum.

Construction of the four-lane vehicular, pedestrian, and bicycle tunnel – known as the Hemphill Street Connector – was awarded to McCarthy Building Companies’ Southern Region under a Construction Manager at Risk (CMAR) contract – a delivery method not often seen within the transportation sector. Under the CMAR delivery model, the benefits to an owner begin in the design phase. The construction manager’s early involvement improves the design through its insights on constructability, value engineering, cost estimating, and schedule. Additionally, unlike other delivery methods, CMAR provides the owner with a skilled advocate throughout the project which also procures the subcontractors who then perform the work.

Construction Management

While long planned, moving the project forward was extremely challenging as there were more than eleven stakeholders to coordinate including TxDOT, Union Pacific Railroad, Downtown Fort Worth, Inc., Near Southside Inc., I-CARE, and multiple others. Further, the project underwent several iterations of design and bidding, and multiple delays during the procurement phase. Under the CMAR contract, McCarthy worked with the City of Fort Worth to align the large group of stakeholders and seek consensus to what was best for the community. McCarthy also assessed all project risks and worked to proactively plan these risks out of the project. The general contractor coordinated self-perform and the subcontractors’ work to achieve the highest daily productivity. The team addressed construction coordination among various subcontractors, evaluated their manpower levels, and ensured they performed their work in accordance to the overall construction schedule. McCarthy also managed the Stormwater Pollution Plan, environmental plans and practices as well as tracked the flow of major materials from initial submittals through fabrication and delivery to coincide with the proper construction sequence.

Construction sequence on the project was vital as it was a multi-phased and complex job with various scopes of work that included a railroad track shift to maintain functionality and other special track work, structural steel bridge construction, deep foundation drilled shafts, waterproofing, earthwork and rock excavation, temporary shoring, rock nail and shotcrete retaining walls, precast panel retaining walls, CIP retaining walls, living “greenwall” retaining walls, storm drainage, concrete pavement, tunnel lighting, street lighting, traffic signals, landscaping and irrigation, metal handrails, signage and pavement markings, and public artwork.

Building Connection

The multi-phased project began with constructing a new rail bridge to support four existing Union Pacific Railroad lines that run through the Tower 55 Rail Intersection at the east limit of the project. With more than 100 trains passing through each day, this is one of the nation’s busiest and most congested rail intersections. To construct the railroad bridge, McCarthy shifted four existing railroad tracks north in a shoofly configuration for each of the separate tracks. The bridge was built in four phases – two adjacent to live rail traffic and two in the middle of active tracks. The bridge beams and deck came in large sections of married pairs or triples with the diaphragms already installed and the deck plates welded on. These sections were very heavy, which, when coupled with minimal space for access, required two crane picks for most segments. For the first phase of bridge, the beams were picked from Interstate 30 which required nighttime lane closures. Remaining phases had to be completed above active traffic.  Additionally, the soil in the railroad right of way was bid as 100 percent TCEQ Class 1 waste. McCarthy was able to segregate, stockpile, and test the soil as it was excavated, and determined that a large portion of it was not contaminated. This resulted in a credit back to the City of Fort Worth of over $1.2M. This action and savings are benefits of working with a CMAR contractor. A hard-bid contractor would have hauled it all off as contaminated, costing substantially more for removal because they would want to get paid the higher unit cost. However, CMAR has a 50 percent shared savings so McCarthy worked hard to mitigate additional costs.

Next, crews focused on excavating under the highway and constructing a four-lane roadway and two 10-foot pedestrian pathways underneath Interstate Highway 30. When excavating the area under the Interstate and railroad tracks, the team encountered extremely hard limestone rock approximately seven feet below grade. Because of that, the excavation effort essentially became a pure mining operation with low overhead clearance and the knowledge that Fort Worth’s main freeway had thousands of cars passing over the excavation site daily. Further, storm sewer lines had to be installed nearly 40-feet deep through this hard rock. This required a large excavator and hydraulic hammer to trench through the rock. The deep trenches require engineered shoring systems and planning for safe access and fall protection.

Finally, it was time to construct the underpass section. Because the crews were working under active auto and train bridges, there were significant shoring measures required, including rock anchors and shotcrete to prevent cave ins. Building the retaining walls and roadway alignment was especially difficult due to the complex horizontal and vertical curvature of the roadway as it descended under the bridges and snaked its way to connect the two intersections. There was no flat plane to be found, and each segment of the walls had to conform to the curves, which was constantly checked by the full-time survey crew on site. Working under the bridges to install the precast wall panels required diligent planning and careful operations to be able to set the panels and place the closure concrete with limited overhead space. The precast walls tied into the existing drilled shafts for support, which had to be exposed and have dowels installed. The drilled shafts for the new bridge were placed with a steel embedded plate at the face. Once the shafts were exposed, nelson studs were welded to the plate to anchor the retaining walls to the shafts. Lastly, the center piers for the new railroad bridge were poured full height, with sonotube formwork to produce a pleasing finish to the columns once excavated and exposed.    

Positive Impact

Infrastructure projects are not typically labeled as “Quality of Life” enhancers, but the new Hemphill Connector – with its vehicular, pedestrian and bicycle tunnel that improves traffic flow and promotes community cohesion – truly moves the neighborhood to a better place. Be it the living green walls, safely lit over-sized pedestrian and cyclist paths, or the public art piece entitled “Flight” by nationally renowned artist Dan Corson, this underpass enriches life and fosters relationships. More and more public entities are choosing infrastructure projects that benefit process and people, in this case, eliminating human barriers and connecting individuals, to the benefit of a refreshed and vibrant community.

During the project, McCarthy worked closely with non-profit organizations that promote the ongoing redevelopment of the Near Southside as a vibrant neighborhood with affordable housing options and safe streets to walk on. The organizations see the district as a destination, rather than just pass through on the way to a different part of town, and they believe that the Hemphill Street Connector will be a strong catalyst for the district’s continued redevelopment by increasing interest from new investors, businesses, and residents.

CMAR for Transportation

From enhancing design through effective constructability reviews, to creative scheduling and overall project management, CMAR benefits civil and transportation projects on many fronts as it facilitates higher quality with on-time delivery at a lower cost. Partnering with McCarthy under a CMAR contract worked well for the City of Fort Worth and the Hemphill Street Connector project because of the Teams Risk Mitigation Strategies:

• coordinating multiple stakeholders
• mitigating unknown and/or unforeseen conditions
• deftly maneuvering through this highly phased project
• leading the franchise utility relocations; both public and private developments adjacent to the work
• supporting public relations and communications, which were paramount; and
• finally, McCarthy created allowances and contingencies and led as a partner and advocate to contend with the project conditions.

The Hemphill Street Connector project was successful in showcasing the benefits of the CMAR delivery method – thru which McCarthy ultimately completed the project five months early and saved the city nearly $4M.

David Wallace, P.E is a senior project manager for McCarthy Building Companies, Southern Region. He can be reached at DRWallace@mccarthy.com.