Retaining Wall Safe Work Method Statement

Under Australian WHS regulations and industry standards, any excavation exceeding 1.5 metres depth requires shoring, benching, or battering to prevent soil collapse before workers enter the excavation. However, best practice recommends assessing each excavation based on soil type, groundwater conditions, and surrounding influences. Cohesionless soils (sand, gravel) may require support at shallower depths, while dry, stable clay may remain unsupported to greater depths. Engage a geotechnical engineer to assess site-specific conditions and recommend appropriate excavation support methods. Never rely solely on previous experience or rules of thumb - each site presents unique conditions requiring professional assessment.

Wet weather significantly increases risks during retaining wall construction and work should be carefully assessed before proceeding. Rain can rapidly destabilise excavations, reduce soil bearing capacity, create slippery work surfaces, and compromise concrete placement quality. Stop work immediately if heavy rain occurs and do not allow workers to enter excavations showing signs of instability including tension cracks, slumping, or water seepage. After rainfall, competent person must inspect excavations before re-entry, checking shoring systems remain secure and excavation faces are stable. Pumping may be required to remove water accumulation. Consider seasonal weather patterns during project planning and schedule critical activities including excavation and concrete work for periods with lower rainfall probability. Temporary covers over excavations or partially constructed walls may allow work to continue in light rain, but always prioritise safety over schedule.

Compaction requirements for retaining wall backfill vary based on wall height, loading conditions, and engineering design. Typical specifications require structural backfill within 1 metre of wall face to achieve minimum 95% Standard Proctor density (AS 1289.5.2.1) with optimum moisture content ±2%. Backfill beyond 1 metre from wall face typically requires minimum 90% compaction. These values assume use of free-draining granular materials with maximum 5% fines. Higher compaction may be specified for walls supporting structures or trafficable surfaces. Testing frequency depends on project size but typically requires one density test per 100 cubic metres of backfill placed. Always compact in layers maximum 300mm thickness as compaction equipment cannot adequately densify thicker layers. If specified density cannot be achieved, review material properties, moisture content, and compaction methodology before proceeding.

Retaining walls exceeding 1 metre in height or supporting surcharge loads must be designed by qualified professional engineers registered with Engineers Australia. For walls in Queensland exceeding 1.5 metres or in other jurisdictions supporting significant loads, engineering design is mandatory under building codes. The engineer must consider soil properties, groundwater, surcharge loads, seismic conditions, and long-term durability. Temporary works including excavation shoring, wall bracing during construction, and construction sequencing plans should also be designed by competent persons with appropriate qualifications and experience. For high-risk temporary works involving excavations exceeding 4 metres depth or complex ground conditions, professional engineering design is recommended even if not legally required. Never construct retaining walls based on generic details or previous experience without site-specific engineering assessment. Inadequate design is a leading cause of retaining wall failure and can result in serious injury, property damage, and legal liability.

Construction workers require various licenses depending on their roles. Plant operators must hold appropriate high-risk work licenses for equipment being operated including excavators (CI class), front-end loaders (CL class), bulldozers (CT class), or rollers. General construction workers require white card (Construction Induction Training) mandatory for all construction sites in Australia. Supervisors should hold construction supervisor qualifications or relevant trade licenses. For concrete work, appropriate formwork qualifications may be required. Traffic controllers working near roads require relevant certification. Workers cannot operate equipment solely based on experience - valid licenses current within expiry dates are mandatory. Site operators should verify licenses before personnel commence work and maintain license register. Equipment operators must understand machine operating limitations, safety systems, and emergency procedures specific to equipment being used. Refresher training should be conducted when introducing new equipment or procedures to site.

Protecting underground services requires systematic approach starting with comprehensive Dial Before You Dig enquiry submitted minimum two weeks before excavation. Review service plans with entire construction team during pre-start meetings. Engage qualified service locator using electromagnetic detection and ground penetrating radar to verify service locations. Mark identified services clearly on ground with paint including service type and estimated depth. Establish hand dig zones extending 500mm either side of marked services where mechanical excavation is prohibited. Expose services using hand tools or vacuum excavation before mechanical equipment approaches within 1 metre. Once exposed, install physical protection over services including timber planks, concrete slabs, or purpose-designed service protectors. Maintain minimum clearances during excavation - typically 300mm for electrical cables and 500mm for gas mains unless services are physically protected. Brief equipment operators daily on service locations and restrictions. Understand that service plans may be inaccurate and services may be located differently than indicated. Treat all excavations as potentially containing services until proven otherwise through careful exposure.