CDC 23 Tunnel
The CDC 23 Tunnel is a 500 LF underground utility tunnel situated in the center of CDC's Roybal Campus in Atlanta, Georgia. The tunnel structure was founded in solid rock and required an extensive support of excavation system (Soldier pile and wood lagging) and removal of over 10,000 cubic yards of Georgia blue granite. The rock was blasted at night in small sections in order to minimize impact to buildings immediately adjacent to the blast zone.
2000 Concrete Structures installed an extensive underslab drain and sump system designed to remove water from the deep excavation during construction and to keep the water levels down once the tunnel was put into service. In addition to the underdrain system, a special membrane waterproofing system (PrePrufe) was utilized to keep the tunnel dry.
The concrete portion of the tunnel structure was constructed in phases utilizing Aluma Systems wall gang forms and 10K per leg scaffolding for the soffit. High-early strength concrete was utilized so that formwork could be cycled quickly. The project was hoisted with a 100 ton crawler crane and all concrete was conveyed by mobile pumps due to access and egress restraints.