Trenching and Excavating Procedures with Safety Considerations

This article was published in the 2024 Excavation Safety Guide.

Trenching and excavating are often at the core of a robust construction site and require proper planning and adherence to best practices to ensure a safe and successful project. It can be among the most hazardous sitework operations. However, disciplined attention to safety standards and procedures can increase job site safety and minimize risk. 

Over the years, the Occupational Safety and Health Administration (OSHA) has increased efforts to define threats and identify safe practices. The good thing is there are safety measures and systems that people in the field can implement to reduce these incidents altogether 

We define excavation as any human-made trench, depression, cut, or cavity involving earth removal. As for a trench? It’s defined more specifically as a narrow underground excavation, deeper than wide. Trenches are, by definition, no wider than 15 feet. What kinds of safety considerations can they pose? Like excavation, they include everything from maintaining structural integrity to watching out for utility lines. Fortunately, a little knowledge can go a long way in supporting safe excavations and earth removal. 

Trenching and Excavating 101: What to Watch Out For 

When trenching and excavating, you must thoroughly understand the most significant risks these operations pose - whether you’re working on installing a trench drain system, digging for utilities, or any other sitework project. 

What is the most significant consideration in excavations? 

Cave-ins are among the primary risks associated with trenching and excavating. Cave-ins account for the majority of incidents. Trench collapses, in particular, account for a significant amount. Besides cave-ins during excavation and trenching, you’ll also need to pay attention to other potential issues, such as: 

• Hazardous atmospheres
• Falls
• Falling loads
• Incidents involving mobile equipment

What’s the best way to guard against these potential hazards? 

For starters, never enter a construction site without the proper protective gear, which includes a helmet, glasses, and vest. As for trenches, don’t enter any that fail to have suitable protective systems in place.

Trenching and Excavation Safety Systems  

A protective system should always be in place for commercial trenches five feet (1.5 meters) or deeper. You can only bypass this requirement when an excavated trench comprises stable rock. When trenches reach a depth of 20 feet (6.1 meters) or deeper, a professional must design their safety systems. This professional must be a registered engineer. You may also rely on tabulated data prepared or approved by such an expert.

What do these protective systems look like?  

Different types of systems exist. They include: 

• Shoring
• Sloping
• Shielding
• Benching

Shoring necessitates installing supports such as aluminum hydraulic or other types to prevent cave-ins and soil shifting. Sloping refers to the technique of cutting back the trench wall at an angle inclined away from the excavation.

What about shielding?

It relies on trench boxes or other support types to avoid sediment cave-ins.

Benching refers to protecting employees from cave-ins by removing earth from the excavation sides to form one or more horizontal steps or levels. This technique usually involves vertical or near-vertical surfaces between levels. There’s a caveat to benching, though. It cannot be used in Type C soils. 

How to Select the Best Safety System 

How do you know which safety system is right for your needs? This decision-making process can be a complicated one, involving considerations such as: 

• Depth of cut
• Soil classification
• Water content of the soil
• Changes due to weather or climate
• Other operations in the vicinity
• Surcharge loads (surcharge loads may include materials used in the trench or spoil) 

Soil Types Demystified 

Soil types fall into one of two categories: granular or cohesive. Granular soils contain coarse particles like gravel or sand. As a result, the dirt doesn’t stick together and will require more extraordinary measures to prevent a cave-in. Cohesive soil types include enough clay or fine particles so the individual particles stick together. As the name suggests, cohesive soil remains less likely to cave in. Besides these essential characteristics, OSHA relies on a “unconfined compressive strength” measurement to categorize each soil type. Unconfined compressive strength refers to the amount of pressure it requires to collapse a specific soil type. Soils are classified as follows: 

• Stable rock • Type A • Type B • Type C

Let’s explore each soil type in greater detail. That way, you’ll develop a better sense of safe and dangerous working conditions.

Daily Inspections by a “Competent Individual” 

Inspections must occur before workers enter the excavation area or trench. This step eliminates the risk of excavation hazards listed above. Who does OSHA define as a competent individual? An individual capable of identifying predictable and existing hazards or working conditions that are considered unsanitary, dangerous, or hazardous to workers. Tasks performed by a competent person include: 

• Testing and classifying soil
• Inspecting protective systems
• Monitoring water removal equipment
• Designing structural ramps
• Conducting site inspections

This individual should be authorized to take speedy action and corrective measures to mitigate potential conditions and hazards. 

Understanding Access and Egress Points 

Your designated “competent individual” will also regularly inspect excavations and trenches to ensure safe access and egress to all excavations. These access and egress points may include: 

• Steps
• Ladders
• Ramps
• Other secure means of exit 

Access and egress safety guidelines apply to all trenches four feet (1.22 meters) or deeper. Means of entry and escape must lie within 25 feet (7.6 meters) of employees. 

OSHA Trench Safety Rules 

What else does OSHA recommend to keep employees safe while working in excavations and trenches? OSHA Trench Safety Rules include: 

• Maintaining surcharge loads a minimum of two feet (0.6 meters) away from trench edges 

• Keeping heavy equipment away from trench edges 

• Knowing where all underground utilities are located 

• Testing for low oxygen, toxic gases, and hazardous fumes 

• Inspecting trenches at the beginning of each shift 

• Never working under raised loads
  
  
• Inspecting earthworks after rainstorms and other precipitous weather 

• Inspecting the trench after any occurrence impacting conditions in the excavation or trench 

• Ensuring that all personnel wear high visibility or suitable clothing when exposed to vehicular traffic 

By following the guidelines above, you’ll ensure the safest working conditions for all employees on the jobsite. Besides following these rules, you must also incorporate preplanning into all potential jobs. 

What Is Pre-Planning? 

Whether your construction company has one year of experience or two decades in trenching, backfilling jobs, and shoring, approach each new job with meticulous preparation and care. What’s the root of most on-the-job accidents? A lack of initial planning. In other words, don’t wait until stepping into the dirt to figure out the best safety system for an excavation or trench. After all, making adjustments to fix sloping and shoring issues will hinder operations, slow progress, and increase labor costs. Putting a band-aid on potential safety issues increases the likelihood of an excavation failure or cave-in over time. With that in mind, let’s review the safety factors you must consider before bidding on a job. 

Safety Factors to Consider Before Bidding 

Before you even start preparing a bid, you must understand safety issues at the jobsite. You’ll also need to know about the materials and equipment your employees need on hand to comply with OSHA safety standards. The following safety checklist will help you evaluate each job site and then draw up a plan accordingly. Factors you must consider include the following: 

• Proximity and physical condition of nearby structures 
• Traffic
• Soil classification
• Ground and surface water
• Location of the water table
• Underground and overhead utilities
• Quantity of protective systems or shoring that may be required
• Weather
  
• Fall protection needs
  
• Number of ladders needed
  
• Other equipment needs

Which processes can help you collect the information you need? They include taking test borings for soil conditions and types, observations, jobsite studies, consultations with utility companies, and meetings with local officials. This research will help you determine the kind, amount, and cost of safety equipment needed for your workers to do their jobs properly, safely, and more cost-effectively. 

Promoting Excavation at Your Workplace 

Trenching and excavation are among the two most dangerous activities at construction sites. For this reason, you must plan for both with a detail-oriented approach. OSHA lays out a comprehensive system of regulations to help you ensure the safety of your workers. From employing a competent person at your jobsite to understanding soil types and safety system implementation, these precautions translate into a safer workplace. Besides following  these guidelines, you must consistently monitor for changing conditions. After all, exposure to vibrations or precipitation can lead to changing soil conditions and the need for different safety systems. Fortunately, with the proper skill set and approach, one can significantly prevent incidents, minimize risk, and effectuate site operational safety.

Ankit Sehgal is the Chief Executive Officer at Swiftdrain, an American trench drain manufacturing company. He has worked on infrastructure improvement projects for the United States Air Force, the U.S. Department of Energy, and the Department of Transportation. For more information, visit swiftdrain.com.