The Camden Street Drain Replacement includes the construction of new drainage infrastructure to alleviate flooding inside the Howard Street Tunnel.
The project entailed constructing two complex shafts (over 50 feet deep) that extended more than 25 feet below the groundwater table. It also involved constructing two hand-mined tunnels under two operational railroads, jacking a micro-tunnel boring machine more than 150 feet, and hitting a receiving collar with only two inches of tolerance, as well as constructing a new stormwater inlet in an active train tunnel. These operations were already challenging but conducting them near an active professional baseball park and football stadium, as well as a convention center that hosts some of the city’s largest annual gatherings, added a new layer of complexity.
Excavation Challenges
The design-build team’s largest challenge involved excavating immediately next to the convention center basement. The team excavated a test trench to identify the location of the existing 48-inch brick storm drain and confirm enough space existed next to the convention center footing to install soldier piles for the support of excavation system. Their initial excavation uncovered that the convention center footing extended two and a half feet wider than shown on the building’s as-built plans, spurring Clark to join forces with the convention center and structural engineer involved in the building’s 1990s expansion. Together, they designed a custom underpinning support system that allowed the team to remove portions of the convention center’s footing and install soldier beams at the originally planned locations.
This project required a highly tailored safety approach that considered underground work, work near active rail lines, and public safety. While constructing the new inlet structure next to active CSX train tracks in the Howard Street Tunnel, crews relied on work windows scheduled between train movements and constructed the base of the inlet structure from inside the 48-inch-diameter, hand-mined tunnel to minimize the impacts of working between active trains. The project also required excavation 25 feet below the groundwater table and flooding was a valid concern. After exploring multiple options, the team installed a chemical grout curtain solution around each shaft, as well as along the alignment of both tunnels below the Howard Street Tunnel, to reduce the potential for flooding and allow the team to overcome the challenge of working below the groundwater table with localized sump pumps.
