Excavation Sloping and Benching: Tips and FAQs

Protecting people working inside trenches and other excavations against cave-ins is critically important, as many cave-ins are not survivable. Excavation sloping and benching are two old, trustworthy methods, along with the more modern methods of shoring and shielding.

Like all protective systems, they aren't the right choice in every situation, but they have their place. For example, they’re appropriate in certain soil types when shoring or shielding isn’t practical.

What is excavation benching?

Benching involves excavating the sides of a pit to create benches, which resemble stair steps. When properly designed and used in the right type of soil, these benches reduce the risk of cave-ins.

Benching must be performed in soil that is classified as cohesive Type B or better. It is never permitted in type C soil due to that soil’s lack of cohesion.

Benching systems typically use a series of benches at different elevations along the excavation wall. OSHA benching requirements limit the height of benches and how far to set back each bench from the one below it. These specs are based on the excavation depth and soil type.

The height of each bench depends on the soil. In type B soil, each step can be no taller than 4 feet, and the lowest bench would have to be cut back 8 feet.

What is excavation sloping?

In excavation sloping, the sides of the excavation are cut so they slope away from the bottom of the pit to reduce the risk of a cave-in. OSHA sloping requirements dictate the angle of the slope based on the type of soil. Steeper slopes are possible with stable soils. Wet soils and less stable soils require gentler slopes.

Getting the angle of a sloped excavation right is critical. If the slope is too steep, the sides are more likely to collapse. If it’s more gradual than necessary, the excavation area will be larger than it needs to be and costs will increase.

The maximum allowable slope is expressed as a ratio of horizontal distance to vertical rise (H:V). The OSHA Technical Manual’s excavation section provides ratios for different soil conditions in excavations less than 20 feet deep. The slope should not be steeper than indicated in this chart, courtesy of OSHA.

Source: OSHA

Type C soil sloping requires the most gradual slopes because Type C soil is the least stable and lacks cohesion. If it shows cracks or signs that a slide is beginning, the soil is in distress and the slope must be cut back an additional 1/2:1.

The maximum allowable slope may need to be decreased if adjacent surface loads or encumbrances such as buildings or heavy equipment are present.

Benefits and challenges of excavation sloping and benching

When used in the right situations and done correctly, sloping and benching can have benefits and also potential drawbacks. The designated competent person for excavation work should be the one to determine the best trench protective system for the project.

Benefits of excavation sloping and benching

Excavation sloping and benching offer several advantages.

• Efficiency: There’s no need to install and remove shoring or shielding equipment.
• Cost (in some cases): Slopes and benches are usually cut with equipment already on site, and they don’t require renting trench protective system equipment. In some applications, including  shallower excavations in stable soil, they can be less expensive than other methods.
• Visibility: The lack of struts and other physical support systems means workers have 360° visibility within the excavation and can move freely.

Potential challenges of excavation sloping and benching

Potential drawbacks of these protective systems include:

• Space requirements: Benching and sloping require more open space around the excavation than other methods. They are not optimal choices for built-up areas.
• Cost (in some cases): Moving dirt around a site can be expensive, especially when the costs of fuel and operator time are factored in. For long trenches, they may not be the most economical approach. The removed soil will have to be reinstated and possibly compacted, and doing so can be costly.
• Timelines: Cutting benches or slopes can sometimes take longer than installing shoring or shielding.

Tips for OSHA-compliant trench benching and trench sloping

In recent years, OSHA has stepped up inspection of excavations. Violations of OSHA’s excavation standards accounted for 9% of the total penalties the agency issued.

If an OSHA inspector visits a site that uses benching or sloping, they may measure the benches or slope to check whether they comply with OSHA regulations.

To stay compliant and keep workers safe, contractors must:

• Properly classify the soil.
• to determine whether sloping or benching is appropriate.
• Cut benches of the required height and horizontal distance. The United Rentals Trench Safety podcast episode on sloping and benching offers in-depth guidance.
• Slope at the required angle. The United Rentals Trench Safety app features a handy excavation slope calculator.
• Have the competent person check the excavation protection system for signs of distress every day before work begins and any time conditions may have changed.

Over decades of use, sloping and benching systems have proven effective when properly designed and implemented under the right conditions. A training course offered by United Rentals’ United Academy®, Excavation Safety Training for Competent Persons, can help competent persons understand when these tried and true methods are appropriate.

For site-specific guidance on trench protective methods, contact the United Rentals Trench Safety team.