Trenching in construction means creating a narrow excavation below the surface of the ground by using an earthmoving machine called a trencher. Trenches are deeper than they are wide, as opposed to a ditch, and more narrow compared to their length, as opposed to a hole or pit.
What’s the Difference Between Trenching and Excavating?
While all trenches are excavations, not all excavations are trenches. An excavation is any man-made trench, cavity or depression formed by earth removal below the ground’s surface, while a trench is any excavation that’s more narrow compared to its length. An excavation can be any shape or size, but a trench generally has a depth greater than its width and a width not exceeding 15 feet.
What Are Trenches Used For?
Trenching is used for a variety of civil engineering and construction projects, such as laying pipes, electric cables, sewage lines or telephone wire. At the residential level, trenching is most often used for digging irrigation or installing plumbing connections, electricity cables and heating system pipes. At the city level, trenching is used to install drainage and sewer lines as well as city-wide electric lines.
Types of Trenches
Different types of trenches are determined by their shape, which depends on the purpose of the trench. The type of trench used in a given project is affected by different factors, such as the type of soil, the size of pipe or other conduit to be installed in the trench, proximity to nearby buildings and the exact location of the trench. All of these elements determine the specific shape of the trench. Here are some of the most common types of trenches:
- Straight: A trench with sides that are parallel and at right angles to the base
- Sloped: A trench with angled sides to prevent cave-ins, commonly used on new construction sites or for installing large pipes or culverts
- Benched: A trench with sides that have been cut away to form steps
- Bell-Bottom Pier Hole: A trench with a top that’s narrower than its bottom, creating a bell shape, often used for footing installations that support a structure’s foundation
As with any construction task involving heavy equipment, trenching can be hazardous and even fatal if not performed properly. Potential trenching hazards include:
- Falling loads, debris or equipment
- Hazardous atmosphere exposure
- Accidents related to earthmoving equipment
- Slip and fall accidents
Compared to other excavation and trenching hazards, cave-ins are not only the most likely to occur, but they also pose the greatest risk in terms of worker fatalities. To reduce trenching risks and ensure worker safety, always follow the OSHA excavation standards adapted below. Note that these apply to all types of excavations, not just trenches.
Install Protective Systems
Cave-ins can be prevented by installing protective systems, and are required for trenches deeper than 5 feet. Here are the most common types of protective systems:
- Sloping: Cutting the sides of the trench at an incline to create a slope
- Benching: Cutting horizontal side slopes in steps (like “benches”) along the trench wall
- Shoring: Bracing the trench walls with a support system made with timber, hydraulic pistons or steel to support the structure until the underground construction is complete
- Shielding: Installing a trench shield or trench box to protect workers from the weight of soil in the event of a cave-in.
The protective system you choose will depend on factors such as the type of soil and water content on-site, climatic conditions, the depth of the cut and proximity to nearby structures. Employers should choose the most practical system that provides the level of protection necessary to keep workers safe.
Pinpoint Utility Lines Before Digging
Starting a trenching project without first locating any underground utilities on-site is extremely hazardous. Workers who are unaware of surrounding utilities risk hitting a gas, water or electrical line before digging, potentially leading to serious injuries or causing a gas leak.
Excavators are required by law to contact local utility workers before undertaking any trenching project — just call your local 811 agency to request that surrounding utility lines be marked before beginning work.
Check Trench Sites Daily
Proper trenching safety includes routinely inspecting a trenching site for potential collapses or cave-ins. This should be completed before the start of every workday and as needed throughout the length of the project. In the event that unsafe conditions are encountered, workers should be removed from the site until proper safety standards are reestablished.
Design Safe Access and Egress Points
Trenches deeper than 4 feet are required to have safe access and egress points installed, such as ladders or ramps. Employers must place them no less than 25 feet from workers on the trenching site when work is underway.
Should You Rent or Buy a Trencher?
The decision to rent or buy a trencher ultimately depends on the frequency of your projects. Remember that you’ll need to consider the same for any attachments, which can be bought or rented separately.
If you frequently use a trencher or excavator in the majority of your projects, investing in one of your own might make the most sense. Remember to factor in the extra costs of owning heavy machinery, like maintenance and repairs.
If you find that you use a trencher less frequently, it likely makes more sense to rent one when the need arises. This way, you only pay for the time you really need, and can avoid shelling out hefty funds for an attachment that you only end up using once. All that being said, the best way to determine the appropriate trencher for your project is to speak with a professional who can look into your specific needs.