Planning for trench shoring

Linear slide rail systems can accommodate the installation of a long pipe over great distances.
Photos courtesy Cooper Equipment Rentals.

Compared to the use of trench warfare in the Race to the Sea during the First World War, more than a century ago, modern trenching does not need to withstand cannon fire—but it is still some of the riskiest work on a job site. Without the right equipment and proper planning, it can be dangerous and costly.

Fortunately, advances in civil engineering, improvements in equipment and updates to safety standards have made trenching work safer and more efficient than ever. An increased awareness of the risks, through additional training and education around shoring systems, has helped crews work with confidence.

Even with these advances, however, trench shoring projects are often complicated and can prove overwhelming. Advance planning is the key to an efficient and safe project, as is access to well-maintained, up-to-date equipment.

Tackling complex projects
Both the construction of new and the repair of existing underground utilities are sorely needed as cities continue to grow and place a heavier burden on their aging infrastructure. Across Canada, provincial and municipal governments have had to dedicate massive budgets to sewer and watermain construction and renovation. By way of example, Ontario has allocated $191 billion for infrastructure, including underground utilities, over the next decade.

Existing buildings, roads, railways and utilities face risks of damage if excavation sites are left unsupported during construction work. As projects become more complex, safety and stability become more critical.

A better understanding of safe job-site and equipment planning is imperative to keeping projects moving forward. Anticipating problems in advance and designing appropriate solutions to them will significantly improve productivity.

Factors like soil type, trench depth and project duration must be carefully evaluated before selecting equipment. While renting the wrong-sized excavator might cause a minor setback, poor planning in design and equipment selection can lead to costlier delays, structural instability and serious safety risks for crews.

Standard, double wall and single wall trench shields can accommodate light- to extreme-
duty underground applications.

Choosing the right equipment
Selecting the proper equipment and following the right procedures during excavation are essential for the safe installation of underground utilities for water, sewer, stormwater, oil, gas, electricity or data. Specialized shoring systems play a critical role in supporting the trench walls, minimizing the risk of soil collapse and ensuring a well-secured working environment for construction crews, to facilitate efficient excavation.

With so many options available, selecting the best fit can be difficult, especially for larger projects. Safety comes first, but avoiding costly delays is also critical and choosing the wrong equipment for working on temporary structures can quickly strain an already-tight budget.

Hydraulic and pneumatic shoring
Hydraulic and pneumatic shoring systems have become the industry standard for working on and around utilities. They can support trench walls near structures, curbs and sidewalks and are suitable for pipe installations where larger excavation equipment cannot be used due to space restrictions.

Hydraulic shoring can be installed and removed with minimal resources from the surface, so a worker is never at risk of being situated inside an unshored trench. Hydraulic and pneumatic shoring both offer versatility in trenches up to 25 ft deep and 12 ft wide.

Trench shields
For light- to extreme-duty underground applications, rental providers may recommend a size-appropriate trench shield. Applications range from sites with shallow or limited space to deeper, more demanding jobs that require medium to large excavators.

In addition to traditional trench shields, modular trench shields are ideal for environments with fewer workers available, as they take less time to assemble and deploy. The use of high-tensile steel allows for several different assemblies to accommodate various site conditions, such as cross utilities and end plating options, all accounted for within tabulated data.

Slide rail systems
Slide rail systems are a common, cost-effective alternative to traditional driven close sheeting. They are made of steel posts and panels. Installing component pieces, rather than larger assembled trench shields, allows for more commonly sized excavators and heavy equipment.

These systems can be used in a number of ways. Four-sided linear systems, for example, are well-suited for long structures, tanks, microtunnelling and boring operations, while a more traditional system is open-ended and can accommodate the installation of a long pipe over great distances.

Specialized equipment
For large projects, the design and installation of shoring systems can be an extensive and complicated process. Specialized trench shoring systems are advantageous for large-diameter pipelines, which demand specific shoring techniques due to their size and depth.

Factors can change quickly over the course of a project, in terms of scope, size or timeline. Equipment that works for one stage may not work for the next. Flexible arrangements with equipment providers will be key to keeping projects on track and controlling costs.

Keeping workers safe
As mentioned, trench work is one of the most hazardous activities in construction. Safety relies on thorough planning, starting with a job-site assessment and an in-field consultation.

Most excavation-related incidents involve workers striking buried service lines. Proper locate permissions from infrastructure owners are non-negotiable. Other significant risks include cave-ins, collapses and falls into trenches. Identifying and understanding these hazards will help mitigate them.

While regulations and industry standards certainly provide essential guidance for selecting appropriate protective measures, no two trenches are alike. Conditions can change daily and will vary across job sites.

Soil classification is a critical consideration when designing a trench system. The stability of any excavation depends on the type of soil and will be affected by such factors as moisture content, consistency, ease of removal, excavation method, water seepage and whether or not the soil has been previously disturbed.

Soil classifications differ by jurisdiction across Canada, but generally can be identified as Type 1, 2, 3 or 4:

• Type 1: Hard, dense and stable. Needs mechanical equipment to excavate it.
• Type 2: Very stiff and dense, but can be excavated with a backhoe easily or by hand with some difficulty.
• Type 3: Stiff to firm and compact to loose in consistency. May be backfill or previously excavated soil.
• Type 4: Loose, soft, wet or filled. Any disturbance significantly reduces its natural strength.

Moisture fluctuations can weaken trench walls and compromise shoring systems. Hence, maintaining trench safety may require constant assessment and adaptation.

Maintaining up-to-date safety training is also essential to creating a secure environment, where workers can perform tasks without the risk of cave-ins or soil movement. It is important to bring in experts to assess hazards, oversee equipment installation and provide training to crews with regard to proper equipment inspection.

By combining proper planning, expert consultation and ongoing training, engineers can mitigate risks and keep teams safe on every excavation project.

More than the right equipment
Designing a trench shoring system is not a one-size-fits-all process. It demands expertise, experience and a deep understanding of site-specific factors, such as soil conditions, excavation depth and surrounding structures. Every project presents unique challenges.

Underground construction and utility installations must be undertaken with safety, environmental protection and the integrity of surrounding infrastructure in mind. Well-maintained, up-to-date equipment is not just beneficial; it may well prove essential.

Cam Dougherty is the general manager (GM) of Cooper Equipment Rentals’ trench safety division, headquartered in Mississauga, Ont.. For more information, visit www.cooperequipment.ca.