An average of 1,000 lost-time trench collapses occur every year, according to the National Institute of Occupational Safety and Health. In 2013, trenching hazards resulted in 30 known deaths nationwide. Authorities estimate that up to 100 fatalities may occur every year, but many are unreported.
We can do better. Trench protection is affordable, and it saves lives. OSHA endorses three basic types of trench protection: sloping, shoring, and shielding. Traditionally in the Great Lakes states, the Midwest, and the East, the prevalent method of protection has been the trench shield, or trench box. Hydraulic shores and components were developed on the West Coast, so that has driven their adoption in that region.
“The trench shield really doesn’t have any limiting soil conditions,” says Michael Ross, national training director for Efficiency Production Inc., a manufacturer of trench protection equipment. “It is a good tool if you have moving or unstable soils, because you have the option to dig inside the box and use the box as a support as you dig down to hold the trench apart. The hydraulic shoring system does have a limitation in that the trench walls need to stand vertical long enough to install the shores. Sometimes the soil is too unstable for the use of hydraulic shoring equipment.
“Each piece of equipment has its own advantages and disadvantages,” says Ross. The most common use of trench shores in laying pipe is where utilities cross the alignment of the trench being dug. The trench shield, or box, won’t allow anything to pass through it. So if you’re in a pipe run where you have a lot of crossing utilities, that would be one reason to go with shores. That’s because the shore has natural breaks in it between the cylinders, which allows the utilities to pass through.
Shoring is anything but a one-size-fits-all way of doing things. When it comes to sizing, flexibility is important.
“Another advantage to shores is the size of the equipment,” says Ross. “A lot of utility companies will carry shores because they take up very little space, and, therefore, they can dig a hole and throw the shores in by hand. You don’t need a separate trailer to carry the box components, because they’re smaller than a trench box. For example, if you had three hydraulic shores, in say, C-60 soil, you could place those six feet apart, roughly. So you could get 12 feet of protected space in a trench. But if you need a 12-foot box, that box would take up quite a bit more space than the three hydraulic shores.”
So shores are lighter in weight and can be installed by hand. They do not require a large machine like an excavator to handle them. Manufacturers publish tabulated data that contain recommendations for the number of shores to use in various soil conditions. Ross says tabulated data for shores is not based on the depth of the trench; the data is based on the placement of the hydraulic cylinders that hold the trench walls apart.
That makes shores very flexible, not only for crossing utilities but also for different soil conditions, Ross says. You can keep collapsing and reinstalling shores, but a box is a fixed object. Shores are adaptable to changes in dimensions, but a trench shield has fixed dimensions. “But with shores, if you don’t exceed the required distance apart of the cylinders, you can arrange those cylinders in an infinite number of places as long as you don’t exceed the maximum distance that the manufacturer’s engineer allows,” says Ross.
“So you can keep shuffling your cylinders around to accommodate not only crossing utilities, but changes like the need to tap into a main or to install something in your trench,” says Ross. “A good example is if you need to find a break in a pipe and you need to dig up to a broken pipe. When you get there, and you’ve got your shores in, the break doesn’t hit the center of the excavation. With a box, you may have to over-dig that on both ends to reposition the box. But with shores, it’s much simpler. You can just collapse the shores and move them over. As long as you stay within the limitations set by the manufacturer, you can move them to suit your needs.
Working to Depths
Ross says the tabulated data for Efficiency Production’s hydraulic shores goes to 25 feet. Shores can only be set by hand to a relatively shallow depth, and if you go deeper, special tools are required to unhook the hydraulic equipment. “The trench shield becomes a more productive tool past 12 or 14 feet deep because it is much more forgiving at those depths,” says Ross. “You don’t have to place it and get unhooked from it once the box is in the ground. You just have to be able to get hold of it.
“Most of the shores you see working are at shallow depths, because that’s where they are most productive: less than about 10 or 12 feet,” says Ross. “They work in all depths up to 25 feet, but as a tool they’re most productive in depths up to about 12 feet. If you’re going to go very deep, you would have very tall shores. And your connection point would be near the top. You can set longer shores with a machine.”
We asked Ross about aluminum shields versus steel. “Your maximum depth and the weight are tied together,” Ross said. “The deeper you want to go, the heavier the box is going to get. So aluminum shields have a pretty good depth rating, but their depth rating is not as good as the same size box made with steel. But aluminum boxes are lighter and you can handle them with lighter machines, such as a backhoe loader. Your aluminum boxes are generally used in shallower depths and are matched to a machine that can dig to that depth.”
Soil Types
OSHA classifies soil into three simple types: A, B, and C. Type A soils are the best: clay, silty clay, and hardpan are examples. Type B soils are intermediate in stiffness-silt, sandy loam, clay, unstable dry rock. Type C soils are the least stable-gravel, loamy sand, soft clay, submerged soil, unstable rock, or soil in which water flows.
When manufacturers’ engineers write up their tabulated data recommending trench protection equipment for various depths and conditions, they further refine OSHA’s soil types. So manufacturers provide tabulated data for trench shields. The data will tell you the maximum depth not to exceed with a certain trench box, and most manufacturers will provide examples. “Don’t take this box any deeper than this depth in that type of soil,” says Ross.
Aluminum might be appropriate for light, one-man operations, but steel is the proper choice for anything larger.
A modular aluminum panel system is lowered into position.
Hydraulic shores work under a different principle. The tab-ulated data will tell you how far apart the hydraulic cylinders can be. “The deeper you get and the more unstable the soil becomes, you just have to put the hydraulic cylinders closer together,” says Ross.
Slide rail systems have vertical rails, and the sheeting slides down between the rails. “A slide rail comes into effect in situations where, for example, you’re setting in a lift station or a manhole,” says Ross. “You’ve got a four-sided system and four-sided boxes are not productive. They’re all hooked together, and you have to take them out all in one piece. So in a four-sided system, there are lots of reasons for the slide rail to become an advantage. Generally you can say that in poor soil conditions, slide rail systems are more productive than other methods such as driving sheeting, or beam-and-plate, or other older methods of shoring. You have to drive the sheeting with a crane, or some other method, and then you have to dig it out.
“But with a slide rail, you install that with an excavator,” says Ross. “It’s all one process. It might seem cumbersome and laborious, but as you’re digging, when you get to the bottom, you’re there. You’re ready to go to work. There’s no additional welding and fabricating, or bracing. It’s just one continuous system from the top to the bottom. Slide rail sheeting all goes down at one time-the rail and the sheeting. When you start, the posts are sticking up in the air, and as you dig down, you dig underneath the components and push them all down as a system.”
Available Equipment
Speed Shore offers a wide variety of shoring and shielding, in both aluminum and steel. The company’s aluminum hydraulic shoring includes vertical shores, waler systems and shoring shields. Speed Shore’s patented “shoring shields” combine the benefits of aluminum hydraulic shoring with the solid-wall security of a static shield. These shoring shields feature “speed struts,” which incorporate hydraulic cylinders and return springs within telescoping steel sleeves. The struts allow for three- and four-sided trench support. Quick-connect pins and hydraulic fittings permit rapid assembly and disassembly, as well as changeover to larger or small Speed Struts.
Speed Shore also offers a modular aluminum panel system, which comprises modular panels, end members, and adjustable spreaders. The system is light enough for transport by pickup truck and can be quickly configured for two-, three-, or four-sided applications. A two-man crew can readily assemble the system by hand for rapid placement in the trench by rubber-tired backhoe or mini-excavator.
Speed Shore’s Aluminum Panel Shields are specifically designed for contractors, plumbers, municipalities, and utilities that generally use a rubber-tired backhoe or a light excavator. These aluminum panel shields are available in a wide variety of sizes and configurations. They have steel lifting and pulling eyes, heavy-duty stacking sockets, and foam-filled walls. A variety of spreader options are available.
Speed Shore also offers aluminum panel shields with a steel frame, which the company says creates the only true aluminum-wall drag box in the industry. The product is designed to work with rubber-tired backhoes or light excavators.
Steel trench shielding is also available from Speed Shore. Standard shields are available with 3-inch to 8-inch-thick walls in a full array of heights and lengths. This line of steel shields includes single-walled shields for less extreme lateral pressures, specially designed manhole shields, and heavy-duty double-wall shields.
Speed Shore’s Tuff-Lite steel trench shields-one of the newest additions to the company’s lineup-are designed for contractors and municipalities that use lighter excavators, but require higher capacities for deeper trenches or poor soil conditions. These shields are available in a full range of sizes and configurations.
Speed Shore’s single-wall trench boxes are designed for use in applications that are usually shallow in depth or where high capacity is not required. They use lower pipe clearance and smaller spreaders, and require lighter machines for lifting and dragging.
Speed Shore says its slide-rail system is a modular, high-capacity shoring system for use in difficult excavations. Double-walled steel panels slide into vertical tracked rails as soil is excavated. The company says the slide rail system offers a cost-effective alternative to “tight-sheeting” methods. Modular components allow for lighter equipment to handle the system, which is designed for utility installations, bore pits, point repairs, tank pits, vaults, and shafts.
This extruded aluminum trench shield features a 2-inch-thick wall.
Trench Shoring Services distributes rental equipment through a nation-wide rental fleet. The company says it stocks more than 35 sizes and strength rated trench shields. Stacking sections for depths to 40 feet are provided out of standard inventory. Spreader width options ranging from 2 feet to 12 feet are available from standard inventory. Special spreaders up to 20 feet wide are made with a minimum of two hours’ notice, says the company.
“We offer a complete line to fit any shoring application,” says Josh Kundel, trench division manager at Kundel Industries. “You can go as light as the hydraulic aluminum jacks, which are designed for a single-man application, up to steel boxes as large as 12 feet high by 50 feet long, that we have built for special projects.”
Kundel says his company is the only one in the industry that solid welds its boxes, supports the outside skin 16 inches on center, uses solid forged steel sockets, has internal pounding members and has an internal stacking system. “Our shield is probably the most difficult in the industry to produce, and we have invested in high-end tooling to make a precision product,” says Kundel.
Trench safety stands on the top step of United Rental (UR) offerings, with more than 50 stores dedicated stores and a support program manned by registered professional engineers to assist with all aspects of a shoring project from initial planning through to job completion. Available products include trench shoring and shielding, slide rail systems, and bedding containers.
In addition, UR offers a variety of professional training courses on subjects, including excavation instruction, confined space entry, safety and fall protection, regulatory compliance, and operator equipment certifications.
UR trains 20,000 contractors a year in the OSHA excavation standard and plans to double that number over the next several years by offering standardized monthly training classes at all its trench safety locations in North America. UR also trains OSHA inspectors; its customers, who receive product- and project-specific instruction; and company employees who assist customers through their branch network.
Sunbelt Rentals offers a wide variety of trench shoring equipment, including steel trench boxes and road plates, aluminum trench boxes, hydraulic shoring shields and vertical shores, aluminum light-shield systems, square and round manhole boxes, water tap boxes, steel bedding/rock boxes and a full line of complementary equipment. Sunbelt also offers a variety of training courses, including one entitled “Competent Person: Excavation and Trench.” The course provides instruction on OSHA regulations and covers a variety of topics:
- Conducting a workplace inspection
- Soil testing and classification
- Various types of protective systems
- Selecting the appropriate protective system
- Preventing accidents and eliminating hazards
Mabey Inc. offers a full line of trench protection equipment, including sheet and frame, slide rail, steel and aluminum trench boxes, hydraulic vertical shores, manhole boxes, and high-arch trench boxes.
Mabey’s trench protection equipment is rated for depths greater than 30 feet in Type C60 soil-and deeper in OSHA’s Type A and B soils.
Mabey’s equipment is made of high-strength steel, which makes it possible to design for most soil conditions, even if groundwater is present.
Highlights of Mabey’s equipment include the following:
- A hydraulic Super Powerbrace System that eliminates the need to purchase, cut, and weld steel frames
- A quick-release piling shackle, with a pin capacity of 8.25 tons, allowing crews to quickly hoist sheets into place
- The excavator-mounted vibrator piling unit, which has a unique design that attaches directly to an excavator to drive sheets, saving time and money
Pro-Tec Equipment offers a wide range of trench shoring and shielding equipment, including hydraulic shoring, aluminum trench shields, light-weight steel trench shields, a main line of trench shields and the Pro HD line of trench shields for use on those projects that require an exceptional depth rating.
Vertical shoring requires high-strength steel.
A hydraulic shoring system holds fast.
The company says its trench shields or boxes are known as the strongest in the industry. Each Pro-Series trench shield includes the industry’s first standard four-point lift system, a full-length double top rail, recessed collar assemblies and a strong cutting edge built from thicker material than the rest of the shield.
The Pro-Tec Equipment slide rail system is the only slide rail system that can provide users with a true clear-span system, the company says. Using external walers with tieback along with sacrificial beams, the Pro-Tec slide rail system is designed to allow contractors to dig the smallest excavation possible while not having to incur the cost of excessive backfill needed with a non-true clear span slide rail pit.
GME offers a complete line of trench shoring and shielding equipment. The range of products includes single hydraulic shores, an aluminum panel trench shield system for light-duty equipment, a 2-inch thick aluminum static trench shield, a 4-inch thick aluminum static trench shield and a range of steel trench shields. The 8-inch steel trench shield is engineered to be best used by excavators weighing between 80,000 and 100,000 pounds.
The GME E+S slide rail system has panels that pivot into place instead of having to be lifted up and over the post to place them, which reduces installation time and enables contractors to use smaller excavators.
Also the GME E+S slide rail system can be used in vibration-sensitive areas such as near hospitals.
The GME MD brace system is the only sheeting and brace system produced in the United States, the company says. It is designed to be used with a variety of sheet piles, and contractors can use their own stock of sheet piles. GME says the MD brace saves money compared to traditional weld and cut systems. And it can be used in conjunction with traditional weld and cut systems for projects that require phasing.
