Underground and Under Budget

Sept. 1, 2009

This is a time of breakthrough after breakthrough in the trench-protection industry. That’s great news for those who champion safety—and it’s also something to celebrate in challenging economic times, as contractors are finding that innovative shoring and shielding solutions are the very reason that underground construction projects are increasingly coming in under budget.

Paul McDonnell, senior vice president of United Rentals Trench Safety, sums it up best in a recent industry white paper when he says that new technologies have expanded choices for excavation support systems and have added a financial incentive for using them. “Unlike conventional trench protective methods that can add time and cost, these state-of-the-art technologies are designed to drive productivity and efficiency. The selection and proper use of optimal trench safety systems have become not only the right thing to do but also the financially sound thing to do,” he says.

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Companies such as Efficiency Production, Foresight Products, GME, ICON Group, Speed Shore, Trench Shoring Services, and United Rentals Trench Safety are some of today’s standouts in the trench-protection industry—and those who have gained a competitive edge by using their new technologies share how and why these systems deliver far greater safety and unprecedented savings in time and labor.

Photo:  United Rentals Trench Safety

Sherwood Construction
The Oklahoma Department of Transportation is working to widen a section of I-44 in Tulsa from four lanes to six. Sherwood Construction is tackling the first phase of construction, a $42 million project in the Perryman Ditch area, where its crews will build a 1.25-mile-long, poured-in-place concrete culvert extending nearly 30 feet underground. As a stormwater drainage system, the culvert starts as three 10-foot-by-10-foot tunnels side by side and expands to three 12-foot-by-16-foot tunnels where it empties into the Arkansas River.

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Sherwood Construction is using a hydraulic bracing and sheeting system supplied by the Rogers, AR, branch of United Rentals Trench Safety. “It’s a new technology from the UK that we’ve brought to the US, and one that will be available through any of our 60 locations,” says branch manager Ed Wernsman, referring to 80T and 150T hydraulic struts manufactured by Groundforce Shorco. “This is a hydraulic system which opens the struts, saving time in installation. The contractor can expand it, then retract it, leapfrog it, and send it on down the line. The hydraulic system saves considerable time and money versus the option of a weld-in-place system, or a bench slope which would have required a 200-foot-plus excavation width, rather than their current width of 50 feet,” he says.

Ron Egge is the office engineer for Sherwood Construction. He estimates that the hydraulic bracing-and-sheeting system will ultimately allow them to finish the 23-month project more than six months ahead of schedule.

“When you’re working in a hole this deep, safety is the biggest issue. In the old days, we used to weld the beams together for support, and there was always that concern over the quality of the welding. Is it good enough? Is it going to hold? With the hydraulic system, we simply drop it in, expand it and lock it into place. It’s certainly a lot easier and faster than having to cut welds out and reweld. It really is the best system we have ever used,” says Egge.

Garney Construction
When the city of Fort Collins, CO, decided to overhaul its stormwater systems, Garney Construction was selected to partner with the city on projects ranging in size from $25,000 to over $15 million. “On each of these projects, Garney has been involved throughout the design process. This has allowed us to provide insight on constructability, scheduling and cost control,” says Jeff Moore, senior project manager for Garney Construction.

Garney’s current project is the construction of a network of detention basins and storm sewers that involves laying 102-inch-diameter pipe at a depth of 30 feet. As such, Garney engineers initially considered tunneling on this project due the great depth. “But then we realized we could save as much as $3.5 million on the first 1,200 feet of pipe if we could find a way to open-excavate it. However, we saw a major problem in using conventional trench boxes. We wouldn’t be able to pull them through the binding sticky clay material,” says Moore, who had been using trench boxes manufactured by GME for more than 20 years.

“GME introduced us to their new slide-rail system, which we rented for a four-month period. It allowed us to dig down in bays, install the pipe, and then advance to the next bay in a leapfrog fashion. It was a quick learning curve to get started and we learned ways to improve on what we were doing day to day,” says Moore.

Photo: CRA
Slide rails from Efficiency Production can be installed easily on a slope by adding a panel on the high side and leaving out a panel on the low side.

According to GME, its slide-rail system offers an open-track system that is more functional than other slide-rail systems. It allows for panels to be pivoted into place, more like a door, and then clamped into the linear rails before sliding into place. This is different from systems that thread panels into closed rails from overhead.

The system’s self-adjusting rollers in a box frame strut ensure that the struts remain level as the excavation from within the trench is made and the slide rail is pushed to grade. GME maintains that this slide-rail system is one-half of the cost when compared to the use of tight sheeting systems, and that fewer workers are required for its installation.

Williams Form Engineering Corp.
Williams Form Engineering Corp. is a distributor for Foresight Products, the manufacturer of the Manta Ray Earth Anchor system, which was recently used on the Guanella Pass road-widening project in Colorado. Thomas Printz, P.E., is the engineering manager for Williams Form Engineering and also heads up his own shoring design firm, Printz Engineering Services LLC. He explains the design approach to this project, which was initially based on soil nail methodology with a GeoBrugg Tecco facing system. “A soil nail is a passive element that relies on a grout-to-ground bond and the strength of the steel element to carry the load of the soil mass that needs to be retained. The earth that is being retained onsite consists of sand, gravel, and large boulders. The grout takes were so large, and in many cases, the shoring contractor [Advanced Foundation Systems] would not realize grout return at the top of the drill hole,” says Printz.

Concerned about the soil nail not performing the way it was designed, Advanced Foundation Systems, along with Printz Engineering Services, decided to use a mechanical anchoring system consisting of Manta Ray (MR-2) anchors and the GeoBrugg Tecco facing to resist active earth pressure imposed by in situ soil and surcharge loading from construction activities.

“The Manta Ray system is an active system, which implies that a load is placed on the anchor, which actively loads the Tecco facing. The facing load produces tension in the Tecco mesh wires to retain the earth between the anchors. This differs from soil-nail wall design methodology, as the soil mass needs to mobilize or move prior to any stress being placed on the nail,” says Printz, who adds that the Manta Ray anchor system is highly successful in roadway fill material applications. “However, in bedrock material, rock bolts are being used to provide the same resistance that the Manta Ray system offers,” he says.

According to Foresight Products, the low-cost Manta Ray anchor system offers significant economic advantages and represents a major breakthrough in “anchoring technology” with a multitude of uses in the utility, civil engineering, and construction markets for utility poles, retaining walls, sheet piles, seawalls, pipelines, erosion control, and underwater applications.

The Manta Ray is driven into the ground, not augured or torqued; neither is a hole dug or drilled. There is no disturbance or displacement of soil. Unlike other anchoring systems, the Manta Ray actually compacts the soil around itself. The anchors are driven with conventional hydraulic or pneumatic equipment that is readily available, says the company.

Photo: Williams Form & Engineering
A Manta Ray Earth Anchor system and GeoBrugg Tecco facing was combined on the Guanella Pass road-widening project in Colorado.

Conestoga-Rovers & Associates (CRA)
Due to a deep grade and a steep incline on a recent excavation project, CRA of Canandaigua, NY, needed a nontraditional shoring system during the installation of six new precast manholes at a shopping center in Dearborn, MI. The six manhole structures were installed at various depth grades ranging in depth from 12 to 25 feet. For each, the challenge was safely and cost-effectively shoring the excavation while also working in some very tight spots.

The traditional shoring methods of tight-sheeting, welded walers, or four-sided trench shields were not applicable, as the excavations needed to be dug on a tight slope or in spots inaccessible for a crane to drive sheeting. CRA also wanted the ability to reutilize the shoring system for all six excavations.

CRA Project Manager Larry Leach chose the rental of a Universal Slide Rail System manufactured by Efficiency Production Inc. The system is a component shoring system composed of steel panels (similar to trench shield sidewalls) and vertical steel posts. According to the manufacturer, it is the only system to offer an open-face rail design on its slide-rail posts. The system is installed simultaneously as the trench or pit is excavated by sliding the panels into integrated rails on the posts—an outside slotted rail first, then an open-face rail on the inside—and then pushing the panels and posts incrementally down to grade as the pit is dug, a process commonly referred to as a dig-and-push system.

Leach says he likes the open-rail design. “After installing 12-feet in the outside rail, it gets tight; but then moving to the open-face inside rail, it’s like starting all over again. There is a lot more flexibility,” he says, adding that he was surprised at how quickly and easily the system is installed and removed. “I don’t think it would be as easy with another type of shoring system. Plus, we soon discovered that one of the biggest advantages of the system is that it can be installed easily on a sharp slope by adding a panel on the high side and leaving out a panel on the low side,” he says.

Efficiency Production engineers say that contractors realize a number of advantages when using this slide-rail system. For example, the installation and required excavation are completed together, saving time and reducing cost. Also, the wall-to-wall workspace is greater and there is minimal vibration to adjacent buildings and surrounding structures. Finally, individual slide-rail components offer the option of using lighter equipment when installing the system. The cost of rental and installation of the system is approximately 50% when compared to the cost of using steel sheeting, says the company.

Trenchless Construction Services
As general contractor for the $3.5 million Sedro-Woolley SR9 Township trenchless sanitary sewer improvement project, Trenchless Construction Services LLC completed one of the first pilot tube projects in Washington state with the assistance of ICON Group, the New Jersey–based slide-rail system manufacturer and distributor of the Bohrtec BM400LS pilot tube micro-tunneling machine.

The project involved pipe being placed under and adjacent to two state highway routes. “Trenchless methods were required because of a lack of detour options to maintain traffic flow,” says John Gustafson, owner and manager of Trenchless Construction Services. “The soil conditions, as well as the accuracy of pilot tube micro-tunneling, made it the preferred method for the 15-inch and 24-inch portions of the project.”

Pilot tube micro-tunneling, also referred to as guided auger boring, was introduced in the 1990s for the installation of small-diameter sewer pipes and water lines. Guided auger boring systems are similar to micro-tunneling systems with the addition of a guidance system, which consists of a camera-mounted theodolite to ensure high accuracy of the line and grade.

The contractor used ICON’s slide rail system to shore a total of six jacking pits, each 11-feet wide by 20-feet long by 14-feet deep. “The ICON slide-rail system is very easy to install, which saved us a tremendous amount of time. It’s also designed and built to withstand the jacking forces of the pilot tube machine,” says Gustafson.

The ICON slide-rail system also features temporary sheeting, which allows the contractor to extract small sheeting panels rather than large shoring panels to create an opening for the pipe installation.

The Bohrtec BM 400LS, with a jacking force of 150 tons and a pull-back force of 75 tons, can perform guided drillings in one-, two-, or three-phase procedures such as pilot drilling, reamer drilling with steel protective piping, alternative reamer drilling with the pushing of product pipes at the same time, and drilling with welded steel pipes.

Photo: United Rentals Trench Safety
It’s best to work closely with the supplier to specify the most suitable system for the job.

Gustafson says that ICON was instrumental in securing the tooling and special equipment required for the pipe sizes on the project. “They were always available for consultation and visited the project site frequently to assure us that we were using the recommended procedures. We were able to complete this first-of-a-kind project for Washington State within the allotted time and without any equipment malfunction delays,” he says.

Safety and Financial Sanity
It’s best to work closely with the chosen shoring and shielding supplier to specify the optimal system for a given application. More often than not, no single solution will fit an entire project, and larger projects typically require multiple solutions. Lastly, remember that today’s new trench-protection technologies deliver a dual advantage—ensuring a safe excavation as well as allowing the contractor to gain greater financial ground. 
About the Author

Carol Wasson

Construction writer Carol Wasson is a frequent contributor to Forester publications.

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Photos courtesy Chino Basin Water Reclamation District.
From left: Matt Hacker, Metropolitan Water District of Southern California; Marco Tule, Inland Empire Utilities Agency Board President; Gil Aldaco, Chino Basin Water Conservation District Board Treasurer; Curt Hagman, San Bernardino County Supervisor; Elizabeth Skrzat, CBWCD General Manager; Mark Ligtenberg, CBWCD Board President; Kati Parker, CBWCD Board Vice President; Teri Layton, CBWCD Board member; Amanda Coker, CBWCD Board member.