Trench Shields Used for Wastewater Improvement in Parking Lot

A contractor was tasked with replacing an existing terracotta sewer pipe with ductile iron in a high-volume shopping center in North Carolina. The project would require two separate excavations of 16-ft length and 6-ft width to depths of 12-ft and 16-ft.  One of the pits would be used as a pipe-bursting launch pit, while the other would be used as a receiving pit.  The contractor’s Competent Person had classified the site’s clay soil as Type C-60.

The project’s location in a busy shopping center created a need for a sound, safe protective system. The contractor wanted a system that could be installed quickly to minimize the disruption to the business activities of the shopping center. After reviewing several protective system options, the contractor elected to use steel trench shields capped with steel plates for the project. Trench shields are a common way of protecting bore and receiving pits for excavations when the soil will stand long enough to allow the shields to be set.

In this application, site engineering allowed a modification of the trench shield design to allow steel plates along the open edges to provide four-sided soil support.  (Note: steel plates cannot always be used to cap the end of a trench shield and the manufacturer’s tabulated data should be consulted for clarification and or a site-specific plan obtained to determine whether it is possible). The contractor was very satisfied with the system and was able to maintain the project schedule while minimizing disruption to the surrounding businesses.