As part of an upgrade at a sewer plant located in the Gulf region, a contractor was tasked to form and pour a new outfall wall. The contractor estimated a 40-ft long, 20-ft wide, and 30-ft deep excavation would be needed to construct the structure. The excavation occurred in previously disturbed clay soil, which the Competent Person classified as C-60. The contractor concerned about project demands reached out to the local NTS branch looking for solutions that could address the active adjacent structures on site, the ongoing poor soil conditions, and reduce the escalating project costs.
After reviewing the needs of the contractor, a site-specific beam and plate system combined with double static bracing was engineered. A beam and plate system is composed of steel plates, and H-beams placed in intervals. Static braces are commonly used in excavations where poor soil conditions are present and extra support is warranted. The beam and plate system can be designed and utilized in one to four-sided applications creating a free span area for contractors to operate.
The site-specific system was designed for excavation of 16-ft, but site changes required the contractor to bench and slope about 45-ft before excavating to the planned depth. Once properly benched, the contractor started the installation process by positioning the steel beams in the ground. The steel H-beams can be installed with either a vibration hammer or inserted into pre-drilled pilot holes. After the beams are positioned, steel plates could then be threaded between the soldier pile flanges. The double static brace wale was placed by a crane and then secured with chains to the embedded H-beams. Utilizing the NTS double static wale braces provided the support necessary for the beam and plate system to handle the surrounding soil surcharge and to accommodate the new structure.
After the addition of the outfall wall, the sewer plant can continue to service the needs of the area. The contractor was pleased with the performance of the beam and plate system and the cost savings using this particular system on this project. While not all excavation projects require a site-specific shoring solution by utilizing a properly designed protective system for a project a contractor can potentially save money and ensure optimal safety for the workers on site.