Site-Specific Shoring for Sink Hole and Replacement of Storm Sewer Line

A Northwest California contractor had been tasked to replace a 96-inch storm drain which failed and created a sinkhole in a busy intersection. The project required a linear run of 133-ft with a width of 14-ft and a depth of 25-ft. The Competent Person on-site classified the medium clay soil as Soil Type-B.

The project site was located adjacent to a busy road intersection. The site required the use of pumps to dewater the groundwater beneath the excavation and the sinkhole area caused by the failing lines. Additionally, the site presented multiple crossing utility lines running above the excavation cut that needed to be secured.

The contractor contacted NTS to discuss a few shoring options. After a careful evaluation of the challenges, the contractor chose the beam and plate shoring system. The beam and plate system with hydraulic struts is a site-specific engineered shoring system designed uniquely for applications with demanding soil conditions and limited access.

The installation of a beam and plate system starts by driving or pushing the beams into pre-drilled pilot holes below the bottom of the excavation. Steel plates are then inserted into the channels of the beams to the desired excavation depth.  For this project, the beam and plate system was paired with a hydraulic strut placed across the excavation. The hydraulic struts provide additional structural strength and balance the pressure of the excavation walls. The contractor was extremely satisfied with the site-specific plan as well as the performance of the system and the service provided by the in-house team of NTS Engineers.