Major Risk Mitigation Strategies Deliver Hospital Concourse with Minimal Disruption

When planning a hospital expansion, there are obvious considerations, such as how many stories the expansion will entail or how to integrate the new build into the existing campus. What’s not common is figuring out how to connect a new underground concourse to an existing level below a seven-story patient tower—more than 200 feet away.

“From the very beginning, the renderings of the master plan included an underground connection. Our team had never completed a tunnel but knew we could make it happen,” said project manager Kyle Allan. “The alternative was to physically cut an open trench through the middle of their hospital to make the connection. It would have severely impacted the existing operations.”

Project team sets the first lattice girder
The project team sets the first lattice girder at the entrance of the tunnel. Courtesy of Brad Pugh

The tunnel will keep hospital foot traffic separated from patient and visitor traffic on the upper floors. Though invisible to guests, the eight-foot-wide underground tunnel will be used by staff to transport critical supplies and materials between the new tower and the existing facility. It will also serve as a mass transit line for lab samples—pneumatic tubes will efficiently whisk specimens across campus.

Through innovative planning and a solution-focused approach, the project team identified potential obstacles for the 200-ft.-long tunnel and took preemptive measures to reduce construction-related disruptions on campus. Before any digging could begin, the first step was to figure out what was under the existing hospital. The foundation, structural supports, electrical connections and pipes had to be considered for the excavation.

Reviewing shotcrete quality
Brad Pugh, Jim Wieser, and Mike Wilson review shotcrete quality at the first section of the tunnel. Courtesy of Brent Elliot

Experienced partners were enlisted to help with the complex scope and underground construction. Blount Contracting and Drill Tech executed the tunneling and Firestop Southwest provided the waterproofing. Brierley Associates, HKS, PKA Architects and Speedie & Associates contributed to the design.

In partnership with the geotechnical engineer, the project team took core samples to understand the soil conditions and scanned the flooring with three different types of equipment to investigate the underground utilities. They identified two sewer lines that crossed the tunnel’s planned path and took major precautions to reinforce, support and protect the pipes.

Drill Tech ties the interior liner
Trade partner Drill Tech ties the interior liner reinforcement after completion of the waterproofing system done by Firestop Southwest in the tunnel. Courtesy of Kyle Allan

“We excavated the earth from inside the hospital and encased the sewer lines in red concrete to make sure they were protected,” said Allan.“The implications of what would happen if we disrupted a sewer line that supported an entire hospital tower would be unimaginable. We had to engineer out the risk.”

To ensure that tremors from the excavation were controlled and safe, predetermined thresholds were programmed into vibration monitors staged along the planned underground path. Allan said the alarms were never trigger by the tunneling work. Construction on the tunnel was successfully completed and the project team is continuing work on the new hospital tower.

Completed look
View looking into the completed structure of the tunnel. Courtesy of Kyle Allan

Allan said close alignment and innovative thinking were key to working around the complicated existing conditions. “Building a tunnel-like this was a pretty wild idea, but we seized the opportunity to help maintain a world-class patient experience. We understood the need and executed the project without an enormous impact to the hospital’s day-to-day operations.”