Shotcrete Safe Work Method Statement

Wet-mix shotcrete involves pumping pre-mixed concrete to the spray nozzle where compressed air is injected to propel material onto surfaces. All ingredients including cement, aggregate, water, and admixtures are combined at the batching plant before pumping. Dry-mix shotcrete conveys dry cement and aggregate pneumatically through hoses to the nozzle where water is added immediately before discharge. Wet-mix systems generate 60-80% less dust than dry-mix processes while achieving superior quality control, reduced rebound (typically 5-15% versus 15-30% for dry-mix), and more consistent strength properties. However, dry-mix systems excel in applications requiring very rapid setting for immediate overhead support or when transporting mixed concrete is impractical. Modern Australian construction predominantly uses wet-mix shotcrete due to superior dust control and quality, with dry-mix reserved for specific applications including emergency ground support or remote locations. Both methods require specialized equipment and trained operators, with wet-mix requiring concrete pumps and dry-mix using rotor machines or dry-mix guns. The choice between methods considers project requirements, environmental conditions, quality specifications, and worker safety including dust exposure minimization.

Shotcrete nozzle operators require powered air-purifying respirators (PAPR) with P3 filters achieving assigned protection factor of minimum 50 due to extreme respirable crystalline silica exposure levels. Standard P2 disposable respirators or half-face respirators provide inadequate protection for nozzle operators working directly in the dust plume where silica concentrations often exceed workplace exposure standards by factors of 50-100. PAPR systems deliver filtered air under positive pressure to full-facepiece or hood protecting respiratory system and face simultaneously. The positive pressure prevents dust infiltration through seal imperfections that compromise negative-pressure respirators. Batteries powering PAPR blower units must maintain charge throughout full shifts, requiring charging infrastructure and spare battery availability. Fit testing is mandatory for full-facepiece PAPR ensuring adequate seal, though the positive pressure provides margin of safety not available with negative-pressure devices. Support personnel including rebound removers and equipment operators may use half-face respirators with P2 or P3 filters if air monitoring demonstrates exposure levels within protection capability. All respirator users require training in donning, seal checking, filter replacement, and maintenance procedures. Clean-shaven faces are mandatory for tight-fitting respirators as facial hair prevents effective seal. Respiratory protection must be worn continuously during shotcrete operations and while dust remains suspended after application ceases.

Control hose whip hazards through comprehensive hose management including proper securing, systematic inspection, predictive replacement, and safe work practices. Secure all hose couplings using safety cables or chains independent of coupling threads creating redundant retention preventing complete separation if threads fail. Inspect coupling threads daily checking for damage, wear, or cross-threading that compromises grip. Replace hoses at specified intervals based on usage hours and manufacturer recommendations, typically 500-800 hours for shotcrete service which rapidly wears hose liners. Mark new hoses with installation date and log usage hours tracking total service time for predictive replacement before failure. Anchor delivery hoses at maximum 5-metre intervals using weighted bags or secure tie-points preventing movement from internal pressure pulses. Position personnel outside potential hose whip radius, calculated as minimum 2x hose length, when pressurizing systems after shutdowns. Route hoses avoiding sharp bends, crossing edges, or contact with hot surfaces accelerating wear. Conduct pressure testing of new hoses before first use verifying rated capacity and detecting manufacturing defects. Install pressure relief valves preventing pressure spikes exceeding equipment ratings during pump surges or blockage clearing. Implement complete shutdown and depressurization before connecting or disconnecting any couplings. Train operators to recognize coupling wear symptoms including weeping at connections, thread damage, or unusual vibration requiring immediate shutdown and inspection.

Shotcrete rebound rates vary with application method, substrate angle, and operator technique. Wet-mix shotcrete typically generates 5-15% rebound on vertical surfaces, increasing to 15-25% for overhead applications. Dry-mix shotcrete produces higher rebound rates of 15-30% vertical and 25-40% overhead due to higher application velocity and less efficient particle bonding. Rebound consists primarily of coarse aggregate particles bouncing off the substrate while cement paste adheres, creating aggregate segregation that renders rebound unsuitable for reuse in shotcrete. Rebound must be continuously removed from application areas preventing incorporation into subsequent layers which dramatically reduces shotcrete quality and strength. Assign dedicated labourers to collect rebound in wheelbarrows or buckets for immediate removal from work zone. Never shovel rebound material back into shotcrete applications regardless of production pressures or material costs. Dispose of rebound appropriately - some projects allow rebound use as fill material away from structural applications, while others require disposal as waste. High rebound rates indicate application problems including excessive air pressure, incorrect nozzle distance, inadequate operator technique, or poor mix design requiring investigation and correction. Optimize application parameters minimizing rebound through proper training, equipment adjustment, and quality materials. Calculate net shotcrete coverage accounting for rebound losses when estimating material requirements and project costs.

Tunnel shotcreting constitutes confined space entry requiring comprehensive controls per AS 2865 Confined Spaces. Conduct atmospheric testing before entry and continuously during operations measuring oxygen percentage (must be 19.5-23.5%), combustible gas levels (must be <5% of lower explosive limit), and toxic gas concentrations including carbon monoxide from diesel equipment. Implement forced ventilation using fresh air ducting supplying minimum 0.3 cubic metres per minute per person in the space. Position ventilation discharge to dilute and remove shotcrete dust, diesel exhaust, and any ground gases. Establish continuous communication between confined space entrants and external standby person using radio or line-of-sight contact. Designate rescue-trained standby person remaining outside tunnel ready to activate emergency response without entering space except with rescue equipment and additional support. Provide emergency egress lighting remaining functional if primary lighting fails. Control diesel equipment exhaust using low-emission engines, exhaust scrubbers, or electric equipment where possible. Implement permit-to-work system documenting hazard assessment, atmospheric testing results, emergency procedures, and authorized entrants before each shift. Restrict entry to minimum personnel required for operations reducing exposure. Brief all entrants on confined space hazards, emergency procedures, and evacuation routes. Maintain rescue equipment including retrieval lines and breathing apparatus immediately outside tunnel. Conduct emergency drills practicing evacuation and rescue procedures before commencing operations. Monitor ground conditions for instability, water ingress, or gas emission requiring immediate evacuation and reassessment.