Strategic Trenching and Shoring

Sept. 10, 2015

Whether a contractor wants to excavate a trench to lay power lines or pipelines, the need for an organized plan of attack is essential. Therefore, an A to Z approach for starting and ending a trenching project is necessary.

Failing to notify the proper utility company or business owner of the intention to dig could have dire consequences. So putting proper planning and safety measures in place before digging the first hole is important to help avoid disastrous results.

First, contact the community stakeholders around the planned excavation project. Any buildings, roadways, railroads, and utilities could affect the trench once it has been dug.

Master everything from OSHA regulations, to high-tech safety equipment in this FREE Special Report: Construction Safety Topics That Can Save Lives. Download it now!

“Responsible contractors do rely on their local utility marking companies and won’t start digging until they have those utilities marked,” says Mitch Post, Mabey Inc. training and development manager. “By doing their due diligence before the project, in many cases, you can get site plans that show where utilities have been installed. A smart contractor is one that knows where those utilities are, relies on the local utility markers, and digs carefully around the utilities.”

Those responsibilities fall on the shoulders of the “Responsible Person,” an individual designated to act as the point person on a project. OSHA defines this as someone who “is trained in the use of various protective methods and soil analysis, is authorized to immediately eliminate onsite hazards, and has knowledge of all OSHA requirements.”

Andrew Schuermann, the trencher and compact equipment product manager for Ditch Witch, has seen his fair share of poor planning. He discusses some of the common mistakes contractors make on trenching jobs.

“Just not having a clear trench path, from the beginning, so that any hazards can be clearly defined and brought to light,” he says. “For example, if I don’t know where I’m going to end my trench and I just start trenching along, knowing I might curve around a building and end up somewhere on the other side. There might be a hazard there that wasn’t marked because I didn’t clearly let the 811 company know where my trench path was going to be. So I might not have a line that’s clearly marked.”

In each state, contacting the utility companies is as simple as dialing 811. Utility companies will come to a site to help a contractor locate and mark utility lines, free of charge.

However, Post warns that problems can arise, even when a contractor reaches out to the utility companies.

“Sometimes those site plans are 20 years old,” says Post. “They’re not always perfectly reliable.”

Following old site plans can cause new headaches for contractors and crews. Accidentally hitting gas or power lines will usually lead to having to pay fines or getting construction permits pulled.

Add Grading & Excavation Contractor Weekly to  your newsletter preferences and keep up with the latest articles on grading and excavation: construction equipment, insurance, materials, safety, software, and trucks and trailers.    

For those times when utility companies drop the ball on accurately locating utility lines, contractors can enlist the services of private utility locator companies to help avoid costly utility line damage. Contractors can also rent or purchase cable locators to help find any hidden utility lines.

Post brings even more reasons for contractors to be cautious. “If you have those things adjacent to your excavation, there are two concerns,” contends Post. “The first is the extra load—what engineers call the surcharge load that those structures put on the excavation. Anytime you dig a hole in the ground, that hole wants to fill itself back in, and it eventually will.”

That means before you dig the hole, account for the proximity of those structures to the project and plan accordingly. Understand that the closer a structure is to the trench, the higher the likelihood of that trench collapsing.

A contractor may hire a surveyor for the project to evaluate the land. This process gives a contractor a good idea of what type of tool the job requires. The type of soil a tool must dig into, and the width and depth of the project dictate what tool a contractor will use.

“It could be a small walk behind trencher for a small utility, sprinkler, or a small electrical line, all the way up to a 300,000 pound excavator that could dig in a 48-inch wide trench, down 25 feet,” explains Josh Brown, an inside sales representative for Protec Equipment.

But Post adds that soil type only matters to a point. “One common mistake contractors make is placing too much emphasis on that soil typing. If you look strictly at the OSHA definition of what types of soil and what characteristics they have, almost anytime you dig, you’re digging in type C soil,” offers Post. “If it’s been previously disturbed, if it’s been dug up before, if it consists of fill, if there’s groundwater present—it’s almost always a type C soil.”

OSHA defines the three soil types as follows:

  • High Stablity—Type A: Clay, silty clay, and hardpan. No soil is Type A if it is fissured, is subject to vibration, has previously been disturbed, or has seeping water.
  • Medium Stability—Type B: Silt, sandy loam, medium clay, and unstable dry rock. Previously disturbed soils, except those that would be classified as Type C. Soil that meets the requirement of Type A soil, but is fissured or subject to vibration.
  • Low Stability—Type C: Gravel, sand, loamy sand, soft clay, submerged soil, dense unstable rock, or soil from which water is freely seeping.

If the type of soil wasn’t enough to worry about at a potential trench site, there are also other potential geological problems waiting for contractors. Shale limestone, sandstone, and other soft to medium hard rocks can slow down a project if a contractor doesn’t have the right tools to handle the job.

Aaron Lewis is the marketing director for Antraquip, a company that manufactures hydraulic attachments for excavators. Hydraulic cutters or “grinders” are commonly used when a contractor needs to cut a trench through a surface containing hard rock. Lewis says these tools save time and money on projects that require any rock cutting to dig a trench.

“Upon talking to a contractor, we actually help them understand the rock hardness, whether we get that through project job-site reports,” says Lewis. Experts at Antraquip can check an in-house database of rock hardness in various geographic areas around the globe. And Lewis says, “If for some reason we do not have any idea what the rock hardness would be in that area, then we would actually fly out there and test the rock. That’s our biggest thing. We want to make sure we properly position the tool for the right application.”

Contractors will generally choose their tool based on the needs of the job. The type of tool they choose largely depends on the width and depth of the trench.

The process of digging the trench can present problems, even if a contractor has planned carefully. Adverse variables can creep into the trenching process.

“They’re non-vibrational. A hammer can be percussive. You got two pieces of metal that slap together that cause an extremely loud percussion. That sends a vibration back throughout the machine, and basically you’re crushing the life out of your machine. Contractors are well aware that hammers are very aggressive on their machines,” notes Lewis. “The grinders are completely opposite. Because there are so many picks and they strike the ground at such a consistent rotation, what ends up happening is you’re not left with the percussion.”

Lewis says Antraquip’s hydraulic cutter cuts down on the noise and disturbance in the local trenching area. “Contractors are really able to see the major benefits of these in urban environments where they actually have sound restrictions. So let’s say they got a project that dictates ‘you guys cannot use the hydraulic hammer because it will fracture surrounding structure’s windows—it’ll put hairline fractures throughout foundations.’ In that case, the only other option, unless they’re going to use hand tools, would be to use the hydraulic grinder to go on and break it up.”

LeRoy Hagenbuch is the president and chief engineer of Philippi-Hagenbuch, the company that manufactures the Rolling Wedge. Like Lewis, he agrees that hydraulic hammers are not an efficient way of breaking up rocks.

His product takes rock breaking a step further and does not even use a pick. He says his Rolling Wedge trencher works in a different way. “The Rolling Wedge is meant for those applications that are challenging. There’s basically two ways to break material: you can either crush it, or you can cause it to be pulled apart. And if you want a large chunk of concrete and you want to break it, if you get a hole in it, it’ll pop.”

The Rolling Wedge is a device that can attach to an existing trencher. Hagenbuch says his product distinguishes itself from others on the market because it avoids violent actions with hard surfaces.

“You don’t have the percussive action of the cutting, of picking. Brute force is what they are using to try to cut through the material. We’re not trying to use brute force. Rolling Wedge has an edge grabbing material and literally pulls it apart,” he says. “Concrete in particular, as well as many other similar materials, has a very low tensile strength compared to its compression strength. So the secret of the Rolling Wedge is to get on something and pull it apart, as opposed to trying to crush it and break it up.”

While the Rolling Wedge can work on any surface, ideally, the machine is meant for harder surfaces. “What we’ve done on this is create something that is meant for the harder, more challenging trenching applications, such as profiling. Basically [something] like frozen ground can be difficult for a normal machine to trench through. We’re probably trenching at 80% or better of the rate as if the ground were unfrozen,” says Hagenbuch.

Still with some trenchers, it’s an either/or proposition. They either cut into dirt or hard surfaces—but they don’t work on both. Rolling Wedge, says Hagenbuch, provides versatility for contractors looking to save more on trenching projects, and anyone looking to trench in soil types A, B, and C. “It allows you to have a cutter you can use more universally than some other of the other cutters out there today,” he says. “It is a product that takes less power to operate than other methods of trenching. It is a product that pulls apart material and takes less energy to do it.”

Once the trench is dug, contractors need to have measures in place to keep workers safe.

According to OSHA, trench collapses kill two workers each month. Facing those harsh statistics can weigh heavily on the mind of any contractor. This is why shoring might be the most important aspect to the trenching process.

OSHA defines a trench as any cut in the earth of at least 5 feet in depth.

Shoring protects a crew working within a trench, from having soil collapse on top of them.

Among the most popular products Brown sells at Pro-Tec are the aluminum hydraulic vertical shoring systems. The basic design of the system is two flat, aluminum rails connected in the middle by a horizontal, hydraulic cylinder, which pushes in each direction applying pressure to the trench walls in order to prevent the soil from collapsing. Hydraulic shoring is popular because it doesn’t require workers to go into a trench to install them. They also help take advantage of a soil’s natural cohesion to keep the trench from collapsing.

According to Post, old school attitudes on trench safety can contribute to on the job fatalities. “OSHA did a 10-year study of excavation fatalities, and in that study they just took a look at every excavation fatality that happened in an excavation collapse in this country, and in 24% of those, they had a protective system and it wasn’t used properly,” he says. “Of all those excavation fatalities, there were absolutely none in excavations where there was a protective system that was properly used.”

Shoring measures are common protective systems for crews working within a trench.

Post says Mabey offers a reliable line of shoring systems. “Hydraulic shoring equipment is a super-versatile system, and it can be used to shore anywhere from small excavations up to very large pits. The hydraulics are what make it very versatile and easy to install. And hydraulics allow you to put positive pressure on the soil. So regardless of the size of your excavation, you can use a hydraulic sheet and frame shoring system to prevent soil movement all the way around and ensure that you have a safe working environment,” he says.

From his experience at Mabey Inc., Post recalls, “In my six years in this business, we’ve never had anything like that happen with one of our customers. It seems a large percentage of excavation fatalities a lot of them were cases where the contractor was not using a protective system—at all.”

Prevention of soil cave-ins isn’t the only worry for a contractor. It’s also important to keep the trench as dry as possible. Sheet piling is popular method of shoring a trench in sandy conditions with groundwater present. One of its biggest advantages is that it minimizes the water that enters the trench. Post has had experience with that as well. “Driving sheet piling is a huge part of the excavation business. That’s one of the more common ways to protect excavations. It’s fast, it’s fairly easy, and it’s very versatile. It’s great to use in areas where there’s groundwater. It’s great to use in areas where there are very high soil pressures from running sands. You can completely close off an excavation with sheet piling. So not only are you protecting workers from the soil pressures and potential collapse, you’re also able to exclude things like water and running sand to keep them from coming into your excavation.”

Joe Moser works as the product manager with Atlas Copco Construction and understands the importance of keeping a trench as dry as possible. “Pumps are critical when trenching and shoring because they remove groundwater as it accumulates, which can happen quickly. Water can loosen soil in a trench, which could cause its walls to collapse if shoring isn’t in place,” states Moser. “Keeping water out of the trench also ensures contractors have a solid and safe surface to walk through, and it gives them a clear view to the bottom of the trench, which is important when digging and placing materials, such as pipes.”

Moser continues by discussing the importance of keeping pumps well-maintained for cost-savings purposes. “It’s a good idea to choose pumps that are built with durable materials, such as double mechanical seals, which provide a consistent, watertight interface. We also offer stainless steel seals, which last longer and are more durable than rubber seals. This makes them great for use on shoring and trenching sites, which can have some harsh conditions. Also look for mechanisms that stop the unit if it overheats or an electric current overloads the pump. On most of our models, the pump will restart automatically after it has cooled. This protects the motor from damage and extends the life of the pump.”

Schuermann, the Ditch Witch trencher and compact equipment product manager, talks more about the hassle of dealing with water that has seeped into the trench. “Rain is big factor. If you get rain overnight, or before you can install your product, depending on your soil condition, whether it was rocky or sandy, loose soil, you’re going to have some runoff back into that trench, either filling the trench with water or causing some of the dirt to sluff off back into that trench, ultimately causing you to re-dig that trench and pull those spoils out.”

Schuermann thinks most of his customers use Ditch Witch trenchers in one day, and don’t encounter problems with long-term trench maintenance. He also says his customers don’t generally use his trenchers to dig holes deep enough for workers to enter. Still, situations arise when a customer needs to do so.

Lewis says his hydraulic cutters not only help to dig trenches, but they also efficiently shore them. “When you actually have a cutter, what you’re left with are perfect 90 degree elbow joints on your trenches, meaning you have perfect vertical walls,” says Lewis. “It doesn’t disturb the surrounding ground, so when you actually go to cut the trench, you’re left with very vertical, straight walls on the side.”

Nick DiPaolo, Sunbelt Rentals’ vice president of sales, says most of his rentals for trench projects are for walk behind trenchers that are generally used with shallow digs, as well as trench rollers to smooth the trench bottom and help prevent its collapse. Some of Sunbelt’s rollersare remote operated, which helps cut down on injuries and tragedies in case a trench collapses.

A bonus for Antraquip’s cutters is the ability to grind rocks into materials that the contractor can later use for backfill.

“Obviously, what you’re hoping, once the product is installed and in the ground, just trying to leave the job site as if you weren’t there in the first place,” says Schuermann.

Hagenbuch agrees. His Rolling Wedge not only provides the cleanest cut of all trenchers on the market, he says it provides the right backfill dirt to finish the job.

“We create a much better backfill material through our cutting process,” says Hagenbuch. “It’s a much smoother material and it’s a much more granular material. It’s not chunky. Backfill material needs to be uniform, it needs to be fairly fine, and it needs to have a nice mix to it.”