A Trench in a Tight Spot

March 1, 2009

St. Francis Hospital in Indianapolis, IN, is in the midst of a $265 million expansion. When completed, the Indianapolis hospital campus will have a new emergency room, six-story inpatient tower, surgical suites, and additional space for support services.

As part of this huge expansion, Tonn and Blank Construction Co. (T&B) is installing a 30,000-gallon fiberglass fuel tank measuring 47 feet in length and 12 feet in diameter. The tank will be used to fuel the hospital’s backup generators.

A project on a busy hospital campus was not going to be easy or routine. The excavation site was located about 6 feet from the hospital, affording limited access and many surrounding obstacles with which to contend, including a loading dock directly along one side that had to stay open throughout the excavating and installation process, and newly installed electrical banks just a few feet on the other side of the excavation site. Excavators and other equipment could only access the site from two sides.

As the construction subsidiary of the Sisters of St. Francis Health Services Inc., T&B adheres to strict safety criteria. Shoring the excavation in line with those standards was going to be a huge challenge.

United Rentals Answers Call
T&B foreman Stan Burnside contacted Jim Wright, branch manager at United Rentals Trench Safety in Indianapolis, to discuss shoring. “After looking at the specs of the project, I could see that our options were very limited,” Wright says. “I contacted Scott Moreland, United Rental Trench Safety’s product installation and shoring specialist, to discuss all of our options.

Because of vibration restrictions at the hospital, the use of a vibratory hammer to install the sheeting and bracing was not an option, according to Wright. “Also, installing a beam-and-plate or lagging system was off the table due to the two-week schedule given to complete the project,” he says. “When it was all said and done, a Slide Rail shoring system really was the best option for the tank installation; it was the most cost effective system for the job.”

After designing a Slide Rail shoring plan, Wright and Moreland called mason, MI-based Efficiency Production-a leading manufacturer and engineering specialist of Slide Rail systems-for proposal drawings for a three-bay, four-sided system that would allow T&B to completely shore an unobstructed pit, 56 feet long and 16 feet wide on the ends, down to a depth of 16 feet.

The Slide Rail components were pulled incrementally from the ground as the backfill progressed.

Designed for Close Work
Efficiency’s Universal Slide Rail is a component shoring system composed of steel panels (similar to trench-shield sidewalls) and vertical steel posts. The versatile system can be used in a variety of configurations, including small, four-sided pits as well as large, unobstructed working pits as big as 50 feet by 50 feet (with Efficiency’s ClearSpan system). The system is likewise suited for use in a linear multi-bay configuration to install lengths of pipe over 40 feet. For T&B’s tank installation project, an unobstructed opening of more than 55 feet was made possible utilizing Efficiency’s unique Parallel Beam cross-trench support design incorporating external ClearSpan waler I-beams.

“When Jim [Wright] first suggested Slide Rail, I was a bit skeptical, because I wasn’t at all familiar with it and it didn’t sound anything like other shoring systems I’ve used,” Burnside says. “But Jim did a great job explaining to me what it is, its advantages, and how it works.”

The Safest Choice
T&B has an exceptional safety record for all its construction projects, and Slide Rail was a perfect fit for the strict requirements of this job. As the trench or pit is excavated, the Slide Rail panels are installed simultaneously, sliding into integrated rails on the posts-either double or triple rails depending on needed depth. The panels and posts are then pushed down incrementally to grade as the pit is dug, a process commonly referred to as a dig-and-push system. Slide Rail is unique in that it is installed and removed incrementally, allowing the trench to be properly shored and safe for workers to be in the excavation throughout the entire installation or removal process.

Overcoming Difficult Conditions
T&B began the excavation by first cutting a pilot hole about 6 feet deep on the end nearest to the hospital and laying in a panel 8 feet tall and 20 feet wide. Eighteen-foot-long Slide Rail corner posts were then set on both ends of the panel by sliding the posts’ outside slotted rails down a t-track welded on the ends of the panels. Two more 8-foot panels were installed perpendicular to the first panel, this time by sliding the panels’ t-tracks down the corner posts’ other set of outside slotted rails, which are 90 degrees to the first.

The excavation’s ground conditions were unique and challenging. Electrical banks had been recently installed along one side, and the soil consisted almost entirely of saturated fill sand. Water almost immediately began flowing into the pilot hole and would have to be controlled by pumps while the Slide Rail components were installed. Putting this system in place was also challenging because the side with sand was very unstable, while directly across the pit was hard-packed clay (next to the loading dock). Fortunately, Efficiency’s Slide Rail is designed to work in both types of soil conditions, even when both are present on the same excavation project.

After the three panels were set in a “U” shape, foot-printing the first bay, T&B brought in the first parallel beam-linear post assembly to be fitted on the ends of the open panels. This cross-trench support is unique to Efficiency’s system and is designed with special parallel beams that pin in place standard trench-shield spreader pipes. The parallel beams have rollers allowing them to be removed, creating a completely unobstructed, shored excavation.

To reach a depth of 16 feet, the panels and posts are pushed incrementally until a depth of 8 feet is accomplished, then more 8-foot-tall panels are installed into the posts’ inside open-face rails, which then are pushed incrementally until the entire first bay is at grade. The second and third bays are installed in a similar manner as the first. After the entire system had been leveled and backfilled at grade, T&B poured in place the tank’s concrete foundation.

High Praise
To assist T&B with the initial Slide Rail installation, Efficiency Production sent Greg Ross, the company’s Slide Rail Systems manager and one of the country’s premier Slide Rail installers. “It’s always interesting to see the reaction of contractors the first time they use Slide Rail,” Ross says. “On the first day, they usually are intrigued on how and if it’s going to work. The second day, there is usually a bit of consternation, as they have to overcome unexpected ground conditions as they are trying to put the system in one piece at a time. But by the third day, they really get the hang of it, and they really start to figure out that this is a great system.”

T&B’s Burnside concurs. “There is definitely a learning curve the first time you use Slide Rail, but once you get the hang of it, it goes in very easily and quickly,” he says. “Having Greg here for a few days really helped in getting the system started going in the ground correctly and helped get my crew into the swing on how to install it.”

After the ClearSpan waler beams were secured in the integrated brackets that slide down the outside face of the linear posts; the three parallel beam-spreader assemblies were removed for the tank set. The result was an unobstructed pit that was 56 feet long and was able to accommodate the 47-foot-long tank. The tank was set with a crane and backfilled with stone, while the slide rail components were pulled incrementally from the ground as the backfill progressed.

The Slide Rail system met Burnside’s expectations. “As we were taking the system out of the ground, I thought to myself that I can use this [system] on another excavation project coming up in a few months,” he says. “In fact, I wish I’d known about this earlier, because it would have worked great on some other utility projects here at the hospital that we’d already completed.”

Multiple Solutions
Since opening the branch in 2005, United Rentals Trench Safety of Indiana has worked with contractors on many engineered trench safety systems throughout Indiana and Northern Kentucky. The Indianapolis branch has done multiple installations with Efficiency’s Slide Rail system in four-sided pit, multi-bay, and ClearSpan configurations. In each instance, the system has saved the contractor both time and money.

United Rentals-Trench Safety is North America’s leading trench-shoring services company, providing safety systems to protect construction workers below ground. A complete line of shoring and trench shielding equipment, pipe-testing equipment, gas monitors, pipe lasers, and trench safety plans designed by a registered professional engineer for complex trench excavations is available through the Indianapolis Branch of United Rentals.

Based in Michigan City, IN, T&B Construction is dedicated to quality, diversity, and flexibility. By streamlining services and maximizing resources, T&B’s experience through the years has earned the company a solid reputation for fulfilling needs as a general contractor, construction manager, and design-build team.

Efficiency Production Inc., “America’s Trench Box Builder,” provides the widest selection of standard and custom trench shielding and shoring systems. Efficiency’s versatile products are designed specifically for safe and cost-effective installation of utility systems and infrastructure improvements. All products are P.E.-certified to meet OSHA and MIOSHA standards.

About the Author

James McRay

James McRay is the Director of Marketing & Media for Efficiency Production Inc.

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