How Construction OHS Prevents Trench Collapses

Trenching and excavation are common in construction, especially when installing foundations, drainage, pipelines, electrical services, and underground infrastructure. But with little warning, the surrounding ground may become unstable, trapping or burying workers. Therefore, to ensure effective Construction OHS, workers must control excavation hazards before entering a trench. The Construction Regulations in South Africa include specific provisions on contractors’ responsibilities when conducting excavation work.

Regulation 13 requires a competent person to supervise the work and assess the ground for stability before any excavation. Contractors must also implement reasonable and sufficient measures to ensure no one is buried or trapped by falling or dislodged material. Preventing trench collapse requires more than an initial inspection. Factors that can affect stability include soil conditions, rainfall, nearby equipment, materials stored around the excavation, vibration, underground services, and changes to the excavation.

Assess Ground Conditions Before Excavation Begins

Preventing a collapse starts before the first worker enters the excavation. Construction OHS must understand the conditions that can affect ground stability so that contractors can plan accordingly. The Construction Regulations in South Africa stipulate that all excavation work be carried out under the supervision of a competent person, appointed in writing.

That person shall consider, to the extent practicable, the stability of the ground before the commencement of any excavation operations. Surface conditions can be assumed to remain stable only if the surface looks solid. Soils and geology react differently to excavation. Other construction work, groundwater, recent rains, adjacent structures, vibration, and services can also influence the excavation.

The rules also mandate that contractors will identify, as reasonably practicable, the location and nature of electricity, water, gas and other services that may be impacted. Contractors must then take all necessary precautions before undertaking excavation work that may affect those services. Consider nearby buildings and roads as well. If excavation will compromise their stability, contractors must implement proper measures to protect the structure and ensure those potentially at risk from the resulting compromise.

Use Appropriate Support and Keep Loads Away From Trench Edges

Preventing sides from falling on workers is one of the most critical Construction OHS controls once excavation has started. The shoring/bracing should be adequate to resist the sides of the excavation. If stability is unknown, professionals (engineering or technical) are needed, not informal judgment.

The periphery is also significant. Loads such as materials, machinery, plant, and other loads can exert additional pressure on the excavation walls. The regulations thus prohibit placing or moving loads where it might cause the excavation to collapse and endanger persons unless suitable precautions are in place. This does not mean excavated material should be stacked wherever it fits, or that heavy machinery should be brought near the trench without considering its potential impact on stability.

Water is also a worry. Rainfall, leakage from services, groundwater, or surface runoff can compromise soil conditions and make them unacceptable. Any water management system should be effective during the work. Workers also need safe access to and from excavations. South African regulations stipulate that access to excavations where people work should be easy and safe, and that access should be located within the prescribed distance from workers.

Inspect Trenches Whenever Conditions Could Have Changed

A trench that was safe yesterday cannot automatically be assumed safe today. Things can happen very quickly, and inspections play a crucial role in Construction OHS excavation management. In addition, all excavations, even those which are braced and shored, must be inspected by the appointed competent person every day before the start of each shift in accordance with the Construction Regulations. Additional inspections are necessary after blasting, following unexpected falls of ground, damage to supports, and rainfall. Maintain an on-site register to record the results. These requirements recognise that excavation stability is dynamic.

Supervisors should monitor for changes that may indicate early instability, including changes in ground conditions, damage to protective systems, water accumulation, movement around the excavation, or other situations that could cause controls to break down. Construction project safety specifications usually extend this to include inspecting for cracks, slumps, bulges, overloaded supports, or water pooling, and to discontinue all entry until hazardous conditions are corrected.

Inspection records are useful because they provide evidence that the excavation has been evaluated and can help identify common issues. However, recording an inspection should never be more important than the inspection itself. Employees should also report changes to the next scheduled inspection, not immediately. If ground movement occurs, supports are damaged, water enters the excavation, or other unusual conditions arise, work may need to be suspended until the risk is reassessed.

Control Access and Strengthen Excavation Supervision

Controlling access to the excavation and supervising it also helps prevent trench collapse. After installation of protective systems, construction OHS responsibilities do not end. The competent person responsible for the excavation operation must have enough knowledge and authority to monitor conditions and take action if they become unsafe. No worker should enter an excavation because work is behind schedule or because it looked safe when it started earlier.

Control of access around the excavation is also required. The Construction Regulations require excavations to be fenced or barricaded with an appropriate barrier or fence if the excavation is accessible to the public, adjacent to a public thoroughfare or public road, or may pose a risk to life. At night or in poor weather conditions, install adequate warning devices. The controls protect the workers and others who might approach the excavation.

Communication is also key. All workers should understand the risks identified in the risk assessment, the controls in place, the agreed access arrangements, and what to report immediately. Supervisors also need to be able to refuse production pressure when safety controls are incomplete. A worker could face the same risk of collapse if he enters an inadequately protected excavation to do a “quick task” as if he were on a longer job. Effective Construction OHS supervision should prevent this scenario and ensure that established excavation controls are not compromised for time or convenience.

Conclusion

Trench collapses can happen instantly, leaving workers little time to get out. To prevent them, it is necessary to control the conditions that make collapse possible, rather than expecting workers to respond when the ground moves. Construction OHS offers a framework for this risk. Take care to control loads near the edges of excavations, as they can cause instability, whether from equipment, material, or plant. Planning must account for underground services and nearby buildings, structures, and roads. Inspection is also crucial, as the site can change.

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