Complex Project Requires Slide Rail Shoring System

November 2009 Vol. 64 No. 11
Chris Acord is the construction manager for Pipeline Utilities Inc.

Pipeline Utilities Inc., Raleigh, NC, had put a bid in for a storm water repair and upgrade project at the University of North Carolina's Boshamer Stadium. The university took advantage of the ongoing renovation of its baseball stadium to also replace the storm water infrastructure that runs below the stadium and ball field.

Pipeline Utilities was charged with removing the existing 60-inch pipe originally installed in the 1970s and now in a deteriorating state; then installing new 72-inch and 84-inch pipe. In order to successfully complete the project, Pipeline Utilities had to excavate 35-feet at the deepest point in poor soil conditions. They were then required to lay 300-feet of the new pipe and set three 14-foot-diameter precast manholes.

In addition to the complexity of the actual construction, the project required a fairly complex shoring system. OSHA requires a protective system on any project where a trench will be greater than five feet or where job site conditions warrant. This requirement helps to ensure that workers can complete their jobs safely through the use of a protective system to guard against or prevent a soil collapse. The intricacies of a shoring system can often go unappreciated until a project such as this demands a more complex planning phase.

The job site conditions that would affect the shoring system began with the soil which is often the first variable that directs the use of a protective system. In good soil, there are many possible ways to shore a system; however, as the soil conditions become worse, the possible options for a protective system become more limited. Generally, as soils become worse, they gain additional weight and exert a greater pressure against a protective system. In addition to the extra weight, as the soils become more granular, they also become prone to raveling.

Excessive soil raveling can prove problematic as a contractor attempts to shore an excavation. While trying to advance the cut of the excavation, the soil will often just fall-in, never allowing shoring to move forward. In these types of conditions, your only option is to shore the excavation continually as you remove the soil.

Depth
In addition, to the poor soil conditions, the overall depth of the excavation further complicated the issue. At 35-feet deep, thousands of pounds per square foot of soil pressure can be exerted upon the shoring system. The deeper the system goes, an increasingly greater pressure is exerted upon the system. This shoring system needs to be engineered to handle the loads at these depths without fail.