Shoring System Helps Military

By James A. McRay | September 28, 2010

Understanding and implementing strict federal accounting and management procedures on government utility projects can be a challenge for some contractors. Chandler Construction Services, Inc., headquartered in Ninety Six, South Carolina, has answered the challenge for more than three decades. With an extensive history of providing quality construction services, Bob Gettys, construction supervisor for Chandler Construction Services, spoke with pride stating, "We continually strive to exceed the military's expectations for quality, safety and production."

Chandler Construction Services is the subcontractor installing a $3-million wastewater treatment plant pump station with effluent force main on Shaw Air Force Base (AFB) in Sumter, South Carolina. Chandler is subcontracting for Webco Construction Company out of Northern Virginia, who was the low bidder on the project let by the Navy's Resident Officer in Charge of Construction (ROICC) — the U.S military's office for all construction projects in the Southeast.

Webco Construction understands the additional protocols of the federal government because all they bid is federal government projects. "It can be very intimidating if you've never worked on a federal government project before," says Nate Engle, Webco's project manager. "I've been very impressed with Chandler's work and their flexibility and willingness to follow the guidelines given them when sometimes they don't understand why the military's engineers want things done a certain way."

Gerald Pearson, the ROICC's civilian construction manager and engineer for the project, works mostly in facility construction. While this underground utility project was new for him, he is very pleased with the progress of upgrades being made to the waste water treatment plant.

The new pump station is necessary due to increased volume at the treatment plant, which is located just off Shaw AFB. The pump station will replace the current effluent force main. However, the 18-foot-wide, 26-foot-long, 22-foot-tall pour-in-place concrete pump station will be hooking in the adjacent existing 24-inch DIP effluent pipe before pumping the wastewater through 30,000 feet of new 12-inch HDPE pipe west to the discharge point along the Wateree River.

The pump station is being installed in a plot of land with very limited space, tucked between railroad tracks and an intersection of two roads. Telephone poles are also present in the vicinity. These cramped quarters pose several challenges for the excavation. A trench could not be sloped due to the proximity of the road and railroad tracks. Normally, Chandler would sheet pile the excavation; however, the close space made it impossible to bring in the required equipment such as a crane and sheet driver. Also the railroad that owns the land would not allow the vibrations associated with sheeting so close to the tracks.

Needing another solution to shore the excavation, Chandler contacted Robbie Belk at MSP Rents in Charlotte, North Carolina, who arranged for the rental of a Safe-T-Shore multi-bay slide rail system.

Safe-T-Shore, a leading trench shield and shoring manufacturer headquartered in Chandler, Arizona, designed and engineered a custom shoring system to fit in the tight quarters between roads and railroad track using their innovative slide rail system. Safe-T-Shore's slide rail is a component system comprised of steel panels and posts. The system is installed simultaneously as the trench or pit is excavated by pushing the posts and panels down to grade as the pit is dug — a process commonly referred to as a "dig and push" system. The stackable panels slide into rails in the posts, either a double or triple rail, depending on needed depth. In the multi-bay configuration for this project, 1-foot-wide parallel beams slide into the inside of linear posts and pin-in-place standard trench shield spreader pipes as cross members — an innovation that increases the system's compatibility.

To install the system, Chandler Construction cut a 4-foot pilot trench and installed an 8-foot-by-24-foot panel, which slid into the outside rail of a 24-foot-tall double-rail corner post. They then added a second corner post to the other side of the panel to construct the short side of the pit.

After this, Chandler slid two 8-foot-by-20-foot panels into the corner posts' rails perpendicular to the first panel, and two 24-foot linear posts slid onto the ends of these. To complete the first bay, 1-foot-by-7-foot parallel beams with spreader collars were slid onto a rail on the inside of the two linear posts, and three 22-foot-long spreader pipes were pinned-in-place as cross members. Panels 4 feet high were stacked on the 8-foot-tall panels in the outer rail. The 8-foot-tall panels were then slid into the inside rails between the corner posts and linear posts on the three shored sides. The bay was then excavated down to a grade of 20 feet.

To install the second bay, this process was repeated with 8-foot-by-14-foot panels added to the other side of the linear posts, and two more corner posts were added to the ends of these panels. Finally, a second 8-foot-by-24-foot panel was added between the corner posts, completing the entire pit's opposite short side. Again, 4-foot-tall panels were stacked in the outside rail and 8-foot-tall panels were slid down the inside rail between linear and corner posts on the three shored sides, and excavated down to the 20-foot grade. The total inside dimension of the two-bay configuration was 24.5 feet by 35 feet 1.5 inches.

The pump station pit was excavated in very wet Type-C soil conditions, and the site needed to be dewatered for a week before beginning excavation. Gettys, who has worked for Chandler Construction for more than 20 years, had used slide rail before, so he was familiar with the intricacies of installing the non-traditional shoring system. "Slide rail really was the best shoring solution for the existing site conditions," he concluded.

The installation of the pump station and wastewater treatment plant upgrade began May 22, 2003, and the entire project is expected to be completed February 16, 2006.