When excavation becomes high risk construction work
Work in or near a shaft or trench with an excavated depth greater than 1.5 metres, or in or near a tunnel, is high risk construction work under the model WHS Regulations and requires a SWMS before work begins. The requirement applies to trenches, pits, shafts, and tunnels on construction sites.
A SWMS for excavation should identify the specific tasks, the soil and ground conditions, the location of underground and overhead services, and the controls for ground collapse, falls, and contact with services.
Ground collapse and trench stability
Ground collapse is one of the most serious excavation hazards and can be fatal. The risk depends on soil type, moisture, nearby loads, and the depth and length of the excavation. Controls include benching, battering, or shoring to prevent collapse, and keeping plant and materials away from the edge.
The SWMS should record how trench stability will be maintained, who inspects the excavation, and how often. Entry and exit must also be planned, with safe access such as ladders or ramps placed so workers in the trench can reach them without travelling more than a few metres.
Underground and overhead services
Contact with underground services such as gas, water, electricity, and telecommunications can cause serious injury or service disruption. Before excavation begins, service locations should be confirmed using plans and, where needed, non-destructive locating methods such as potholing.
The SWMS should describe how services are identified, how work near them is controlled, and what happens if an unexpected service is found. Overhead services near plant and equipment should also be addressed, including maintaining exclusion distances.
Access, egress, and water management
Safe access and egress are required for any trench a person enters. Spoil piles, plant, and stored materials should be kept back from the edge to avoid surcharging the trench walls. Where water is present, dewatering may be needed to keep the excavation stable and the surface safe underfoot.
The SWMS should set out the access method, the exclusion zone around the trench, and the inspections carried out before each shift and after any change in conditions such as rain.