If a form or other structure installed or constructed in an excavation decreases the space between the form and the side of the excavation to 15 feet (4.6 m) or less (measured at the bottom of the excavation), the area is also considered to be a trench. Recent technology has made possible the engineering of trench shields that are lighter and capable of handling greater loads. Contractors are able to use even smaller machines to install these shields, allowing for the design and installation of much larger pipeline projects.
Shoring is the provision of a support system for trench faces used to prevent movement of soil, underground utilities, roadways, and foundations. Shoring or shielding is used when the location or depth of the cut makes sloping back to the maximum allowable slope impractical. Shoring systems consist of posts, wales, struts, and sheeting. There are two basic types of shoring: timber and aluminum hydraulic.
Hydraulic shoring, which uses a prefabricated strut and/or wale system manufactured of aluminum or steel, appears to be the trend today. Hydraulic shoring supplies a critical safety benefit over timber shoring because workers do not have to enter the trench to set up or remove hydraulic shoring. Hydraulic systems are light enough to be installed by one worker, are gauge-regulated to ensure even distribution of pressure along the trench line, and can have their trench faces preloaded to use the soil’s natural cohesion to prevent movement.
They can also adapt with no trouble to various trench depths and widths. Shoring ought to be installed from the top down and removed from the bottom up. Hydraulic shoring should be checked at least once per shift for leaking hoses and/or cylinders, broken connections, cracked nipples, bent bases, and any other damaged or defective parts.
Pneumatic shoring works in a way comparable to hydraulic shoring. The main difference is pneumatic shoring uses air pressure in place of hydraulic pressure with pneumatic shoring having the drawback of an air compressor required onsite.
Screw jack systems differ from hydraulic and pneumatic systems in that the struts of a screw jack system must be adjusted manually. This creates a hazard because the worker is required to be in the trench in order to adjust the strut. In addition, uniform preloading cannot be achieved with screw jacks, and their weight creates handling difficulties.
Single-cylinder hydraulic shores are generally used in a water system, as an aid to timber shoring systems as well as with shallow trenches where face strength is vital. Underpinning involves stabilizing adjacent structures, foundations, and other intrusions that may have an impact on the excavation. This procedure involves physical reinforcement of the foundation and should be conducted under the direction and authorization of a registered professional engineer.
Trench Boxes differ from shoring because they’re intended mainly to guard workers from cave-ins and related incidents. The excavated area between the outside of the trench box and the face of the trench should be as small as possible. The space between the trench boxes and the excavation side are backfilled to prevent lateral movement of the box. Shields may not be subjected to loads exceeding those the system was designed to withstand.
Trench boxes are normally used in open areas, but they also may be used in combination with sloping and benching. The box should extend at least 18 inches above the surrounding area if there is sloping toward excavation. This can be done by having a benched area adjacent to the box.
Earth excavation to a depth of 2 feet below the shield is permitted, but only if the shield is designed to resist the forces calculated for the full depth of the trench and there are no indications while the trench is open of possible loss of soil from behind or below the bottom of the support system. Conditions of this type require observation on the effects of bulging, heaving, and boiling as well as surcharging, vibration, adjacent structures on excavating under the bottom of a shield. Watchful visual inspection of such conditions is the main and most sensible approach to hazard detection and control.
Trenching work has a notoriously poor safety history, especially in this country. US Bureau of Labor Statistics (BLS) data show that 271 workers died in trenching or excavation cave-ins from 2000 through 2006. A review of multiple national databases by the National Institute for Occupational Safety and Health researchers found trenching and excavation hazards during construction activities resulted in 488 deaths between 1992 and 2000, an average of 54 fatalities each year.
Sixty-eight percent of those fatalities occurred in companies with fewer than 50 workers. Forty-six percent of the deaths occurred in small companies with 10 or fewer workers. The sad fact remains that hazards associated with trench work and excavation are avoidable, yet injuries and fatalities linked with these hazards persist. Regulations and consensus standards clearly describe engineering controls, protective equipment, and safe work practices to minimize hazards for workers during trench work and excavations.
Safety and efficiency may be viewed as being closely related. The cheapest methods of laying down underground piping may not always be the safest and this may also make the method less efficient. Any recent drops in trenching fatalities in the last few years may also be related to the fact that the economic downturn has meant fewer trenching jobs and projects. In the end, good equipment and knowledge of the risks as well as how best to avoid them will keep everyone safe and get this important underground work done.
Keeping the Trenchers Moving to Guarantee Productivity and Safety
Vermeer manufactures the rubber-tracked, rubber-tired, and steel-tired trenchers. That is one of their many product lines built. This equipment is able to handle open-cut and trenchless installations for utilities and other services. Vermeer trenchers can cut anything from a 4-inch trench 2 feet deep all the way to a 3-foot trench 20 feet deep in solid ground. Utility installations are their primary work: gas pipelines, electric lines, fiber optics, or anything that needs to be put in the ground. The company has been in the trenching business for over 40 years.
For cutting through rock, carbide-based, bullet-shaped teeth on a rotating chain do the work. “We make a wide variety of trenchers to meet a wide variety of applications,” explains Jon Kuyers, global product manager for Vermeer’s Underground Equipment Group.
“If you are trenching in solid rock it is going to require one type of machine, and if you are installing farm drainage it is going to require another type of machine. If you are putting in any type of utility service to your house, as well as if you are an excavator specializing in utility placement, we build those types of projects, too.”
Because the ground varies in so many different parts of the world, and because trenching can vary with the seasons, Vermeer makes sure its trenchers can work in all different types of conditions. Whether frost in northern Minnesota, solid rock in Nevada, or sticky clay in the Carolinas, the company has designed its products to meet all different sorts of ground conditions efficiently and with good reliability.
“With our dealers throughout the world, we like to say, “˜No matter where your customers are, talk to your local dealer because they know the ground conditions best in that area.’ We do a lot of collecting line trenching in such areas as Wyoming.
“Depending on the type of soil, a machine will be set up with a certain type of chain to maximize productivity and minimize operating costs. In Texas, I would run a mining chain with carbide teeth that will cut the ground easily without a lot of damage to the machine; if I’m trenching in central Illinois, I’ll use a different type of chain cutter to maximize my productivity, ensuring the most amount of footage per day.
“We are a narrow-width trenching company. With safety we look for operator pinch-points to protect them from the digging chains or augers, make sure hydraulic lines are not exposed to the operators, and a whole host of other safety regulations we consider during design considerations to make sure our equipment is the safest it can be.”
The Vermeer TrenchSense system is integrated into a lot of the company’s trenchers. If the chain stops, the computer on the machine reads the engine’s amount of rpm drop and automatically stops the digging train by reversing it. The computer then backs the machine up just a little bit and re-engages the chain without the operator touching any lever. When trenching on less-than-desirable ground, this has made a huge impact on productivity for the operator, according to Kuyers. Now there is no more engine rpm drop or stalling out by the machine.
“We always ask our operators to review the owner’s manual to make sure they know how to operate the machine,” he says. “A lot of our dealers do training, making sure the operator is capable of handling the job. Dealers help coordinate and set up training.”
Hydraulic Shoring a Good Fit for Energy Production Projects
Since the preference now is to have energy pipelines out of sight, there is more call to have pipelines buried, according to Tommy Marciniak, marketing manager with Trinity Shoring Products Inc. His company has been around since 1995, and its national dealer network has many independent dealers dealing with end users. In Michigan, one Trinity Shoring subsidiary, ProTec, has three marketing managers that deal directly with the contractors. “We’ve shipped overseas to Jordan, Australia, and to five of the seven continents with our products,” explains Marciniak. “The only two continents our products have not been used in are Antarctica and Africa.
“In addition to being a safety tool-protecting the lives of workers-our product can be used as a production tool, too, to increase the amount of pipe actually laid per day. The ProBrace is a hydraulic sheeting that is a perfect fit for high-production work in addition to being safe; this is our newest product meant to be a factor in installing pipe as opposed to the use of sheets and frames, lags, or sheet piles. It even works for large-bore projects such as those involved with digging beneath a highway.”
ProTec is tied into all the Caterpillar rental store dealerships on their national accounts, according to Marciniak. In mining applications the uses are mainly aboveground. Customers both buy and rent the ProTec equipment. “In certain regions of the country contractors simply want to purchase the shoring products,” he says. “With our dealer network it helps us that we are able to sell directly to our dealers, and the dealers can rent or sell directly to our customers. We are also able to rent to our dealers so they can rent to our contractors. Some of our equipment in Michigan is over 10 years old. The life span on the equipment depends on wear and tear as well as how good the maintenance is on the products. By not abusing the equipment, taking good care of it, it can last well over 10 years.”
The shoring products should be inspected before going to the job site and after they have been onsite. “The introduction of the ProBrace System, a hydraulic brace system-which can be coupled with existing sheet pile systems-allows for larger excavations to be put in place. With larger projects and larger tank installations, this makes working in such holes easier compared to the traditional welding and cutting installations, which are immobile. This is brand new as of the last quarter of 2012.”
One of the perks of the system is that it allows contractors to use existing sheet piles with the system if the hydraulic ramps are rented or purchased from ProTec or ProTec dealers. “We try to keep things as simple as possible,” adds Marciniak. “Our new ProTec bracing system has been under development for the past year and a half. Much of that work went into keeping it as simple possible for our busy end users.”
Is It a Production Tool, or Is It Safety Equipment?
Cerda Industries is a trench shielding and shoring manufacturer, in business for some 14 years. In addition to custom fabrication services, the company manufactures trench safety products, including trench shields, square manhole boxes, “Pipe Tiger” pullers, and other equipment.
The company’s static trench protection systems cover a wide variety of applications and depth requirements. Many models range from a lightweight 3 inches up to 8 inches and higher in wall thickness to help with deeper excavation needs. Trench shielding is the most common method of trench safety protection in the industry. Lightweight aluminum shields are one of the most common products used when excavator size is a factor and excavation safety requirements exceed aluminum hydraulic shoring.
Such drop-in-place lightweight shields work with rubber tire backhoes or mini-excavators. Durable, lightweight shields fill the gap between hydraulic shoring and large steel trench shields.
Aluminum hydraulic vertical shores are perhaps the most cost effective way to shore excavations where more stable soil conditions exist.
The units are designed to be used in linear applications where the shores can be installed and removed from above the ground at the rate of the excavation process without ever entering the trench. This versatile system applies active pressure to the face of the excavation, allowing for less movement of the surrounding soils.
G1 & G2 Sheeting Guide Systems are innovative products combining conventional slide rail panel systems with integrated vertical steel sheeting. The G1 & G2 sheeting systems are some of the most cost-effective and efficient systems on the market today when it comes to crossing utilities, according to Dan Williamson, who has some 35 years in the industry.
“The systems can be used in both linear and pit-style applications,” explains Williamson. “These systems are a great alternative to conventional sheet piling requiring vibratory hammer systems to install the sheeting. The proprietary designed cantilever sheeting allows you to dig and push the sheeting to desired depths and stop where crossing utilities encumber the excavation. In most applications the G1 & G2 systems can installed without a waler at the bottom and only with a 2-foot toe-in of the sheeting.”
The Pipe Tiger can perform dead weight pulls (or drag pulls) based on the weight, the diameter of pipe, and the amount of friction between the pipe and the ground. Standard features of this unit include a “quick pin” telescoping over-sleeve for different sizes of pipe, an inner-sleeve tension device to reduce the slope of the telescoping member, a fully automatic onboard battery charger, and a “warn” winch thermo-relay that shuts down automatically when the unit is overloaded.
“My time in this industry has shown me that trenching, shielding, and shoring products are not necessarily a production tool, but actually more of a safety product,” adds Williamson. “This is because OSHA guidelines exist concerning their use.
“We’re all about safety and trying to come up with innovative items; we don’t like to follow anybody but to come up with our own. Everybody’s trench box is the same-it just comes down to a couple little different things.”
The Cerda Industries website shows a huge John Deere tracked excavator resting just outside a guy-framed area while its bucket does the work inside. These G-1 and G-2 guy-framed portable systems are some 20% more cost-effective compared with sheet-piling systems, according to Williamson, in addition to being an alternative to sheet-piling systems. This innovation of theirs is now on a number of job sites in Panama and other places in Central America.
“We find that the most important thing in what we do is to listen to our customers,” adds Williamson. “It’s vital we don’t sound like we know it all; we try to adapt to what they want-something different and we’re open for it. Listen to other people’s ideas-especially contractors-about what they want. After listening, we adapt and are very flexible.
“Our company is relatively new but I have 35 years in this industry as do others with the company. We are among the major manufacturers in this industry with which we work; there are plenty of smaller ones to doing this important work. We work with some of the United Arab nations and other countries, including Brazil, where there are billions of dollars worth of projects going on right now. Cerda also has a major strategic agreement with one of the largest rental companies on the market; we’re not the largest of the top companies, but we are on the list.”
With Options for Safety and Peace of Mind
There are three different types of trench shielding, with the third type something of a hybrid, according to James McRay, director of marketing with Efficiency Production Products Inc. The first is the traditional trench shield, which consists of a steel sidewall with pipes creating a sort of box commonly referred to in the industry as a trench box. Workers laboring in the trench box area are shielded from wall collapse. This is sometimes called passive shoring in that it doesn’t do anything to prevent other portions of the trench from collapsing.
The second type is hydraulic shoring, which prevents collapse by applying hydraulic pressure through a cylinder connected to aluminum rails. When activated, it creates a pressure arc to the sides of the trench.
Hydraulic shoring also has a couple of variations, some that run vertically and some that run horizontally. Some are designed specifically for trench rescue operations-called rescue shoring. There is also hydraulic shoring that is designed for height clearance.
Systems using steel panels and steel posts, similar to trench shield fly walls, may be applied vertically. These are installed from the top down in a dig-and-push process. A little bit of digging is done, and the shield is pushed down. Technically this is shoring, and it has become very popular with underground contractors. It is extremely flexible to be able to take panels and posts and put them in all different kinds of configurations. There are a lot of different variations.
“Now that we have perfected our premiere slide rail system, we’re adding ways to make it easier for the contractor to install the slide rail in different places,” says McRay. “This is using innovative equipment like our ground quick-release shackle. Shackles are normally screwed in using a ladder. With this system, no one has to climb up on a ladder anymore, making the process much faster.”
Although the company’s sheeting guide frame has been around for a number of years, it now has been integrated into the slide rail. This new system is called Shor-trak. The sheeting guide frame slides onto the post like a panel and then 86 overlapping sheets can be stood up and pushed into the ground. This has been improved even more with the company’s panel guide, which gets the sheeting crane further down into the excavation.
“This is a safety tool, but we’ve always considered it a production tool as well, with the contractor in mind,” adds McRay. “In the absence of that trench shield, you would have to slope your trench in order to make it safe at the same time excavating way more dirt, which costs more money and slows you down.”
Regulations and consensus standards describe engineering controls, protective equipment, and safe work practices to minimize hazards for workers during trench work and excavations.
Meeting the Construction Needs
Mike Garland, general manager with Direct Equipment in Ontario, uses Slide Rail and ProBrace and has been shoring up trenches for some 40 years. “The Trinity Shoring Products’ ProBrace System is fairly new for us,” explains Garland. “We don’t really do beam and lag. Things have slowed down; the private funds have dried up in recent years. A lot of the money was from joint ventures, but now the federal government here in Canada is putting a lot of funds into transit projects; it’s a lot like Los Angeles-there’s a lot of problems with transit. That’s been the government’s focus for the last couple of years.”
This is a competitive business, largely a matter of where the equipment is going, according to Garland. “The pipeline people tend to do their own thing. There are a lot of different outlooks when it comes to developers, fixing foundations or whatever you are dealing with. There is a broad array of people involved in shoring up.
“We did one of ProBrace’s first setups; we’d been waiting on a couple of jobs to try these braces to see if it was a good fit. This one happens to be at the busiest intersection in North America, right here at Highway 401 in Toronto. They are augering across 10 lanes of highway to install a pipeline.”
Working Out Solutions
Steve Betsko, operations and project manager with McDaniels Construction, has been involved with Efficiency Production products for some five or six years. McDaniels specializes in site work, concrete, and infrastructure. The firm is strictly limited to the state of Ohio. From a constructability standpoint, the Efficiency Production Products are an excellent source of shoring solutions. “Typically I will send my guy, who is Mike Ross, send him a sketch-maybe detailed, maybe something from the back of a napkin-and say here’s my condition, my situation,” explains Steve Betsko.
“We’ll then ask, “˜can you help us with a shoring solution?’ They have a great design and engineering staff that understands underground work, and at the same time they apply their understanding of underground work and what kind of equipment and tools you’re using to the kind of product they will send you a picture of and say, “˜This is going to work.'”
They’ll assist Betsko with a shoring solution based on information they provide and their knowledge of their own systems. “Their equipment is modern, good, and it keeps my people safe,” adds Betsko. “They react quickly to changes in the situations and do a nice job for us. In the end, it’s all about keeping people safe.”
In the Midst of Shifting Sands and Moisture Contents
Wally Hoffman, superintendent of Dallas 1 Construction, just outside Tampa, FL, does underground utility work. Trench safety is the No. 1 concern for his company, and Efficiency Production products maintain that safety. “The boxes we use are just regular trench boxes with two sides and bars on the end so that nothing collapses. We also use four-sided boxes that are simply dropped in the hole and you go from there.
“We’ve used other people and have had our own boxes, but lately with the many pipe jobs we’ve had we’ve been using their material and their product. We work in Florida where, with soil that is either wet or sandy, the biggest challenge is trying to keep it dry so you can keep working on the hole. Being wet in the sandy soils means the holes always want to cave in. That’s the reason that, out of all the boxes, we’re using that one.
“The pipes we install are carrying sewer, water, and stormwater reclaim pipe, and then we install boxes and manholes and anything involved with those functions.”
