A contractor had been tasked with installing an effluent distribution box between two existing structures at an Eastern North Carolina wastewater treatment plant. The project would provide a 50% increase in the daily processing volume for the municipality, while also reducing energy costs 20%.

The effluent distribution box and related slab would require a very large excavation and for that excavation to be about 30-ft deep. Unfortunately, due to the excavation’s size requirements and the limited space between adjacent structures, there wasn’t space to excavate for the conventional four sided excavation system. A few four sided systems could be installed within the space requirements, however, once installed the need for crossing struts and or corner bracing wouldn’t provide the contractor with the necessary free span clearance to complete the project.

The contractor reached out to National Trench Safety to discuss this project and to see what solutions might be available. Using a site specific engineered plan, National Trench Safety developed a plan to provide a free span, round excavation. The system was designed using a high strength, interlocking steel sheet along with welded in place wales according to the engineered plan. The inherent strength of the circular design along with steel sheets allowed the design to provide the contractor with the necessary free span working room to pour the slab and install the effluent distribution box. Additionally, the steel sheeting design would facilitate the need for lines to be run from the effluent distribution box and out of the shoring system’s boundaries. Sections of the sheeting could then be cut to allow the passage of the pipe while not sacrificing the strength of the system, when following the engineered plan.