Here's a comprehensive list:
1. Safety Precautions
Fall Protection: Ensure workers are protected from falling debris or rebound material. Use proper scaffolding, platforms, or manlifts.
Ventilation: Maintain adequate ventilation to remove dust, rebound, and fumes, especially in confined tunnel spaces.
Personal Protective Equipment (PPE): Workers should wear helmets, goggles, respirators, gloves, and protective clothing.
Stability Check: Assess the stability of the rock or surface before spraying to avoid sudden falls or collapses.
2. Surface Preparation
Clean Surface: Remove loose materials, dust, oil, and water from the surface. A clean, damp (not wet) surface ensures better adhesion.
Anchoring Mesh: If using reinforcing mesh or rock bolts, ensure they are securely fastened and properly positioned before spraying.
3. Mix Design and Consistency
Correct Water-Cement Ratio: Maintain a proper water-cement ratio for optimal pumpability and adhesion.
Additives: Use appropriate admixtures (accelerators, retarders, plasticizers) depending on tunnel conditions like temperature or shotcrete thickness.
4. Spraying Technique
Nozzle Distance and Angle: Keep the nozzle 1–1.5 meters from the surface, at a 90-degree angle, especially on the crown to ensure good compaction and minimal rebound.
Layer Thickness: Apply in thin layers to avoid sagging or delamination. Multiple passes may be necessary.
Even Coverage: Move the nozzle steadily and evenly to avoid over-thick or thin areas.
5. Rebound Management
Control Rebound: Use correct spray angle and nozzle velocity to minimize material rebound, which is higher on overhead surfaces.
Rebound Removal: Do not reuse rebound material; remove it promptly to maintain quality.
6. Curing and Setting
Initial Set Monitoring: Allow for initial setting before applying subsequent layers or exposing to heavy vibration.
Curing: Apply appropriate curing methods (e.g., mist spraying or curing compounds) to prevent shrinkage and ensure strength development.
7. Machine Maintenance
Equipment Check: Regularly inspect and maintain the wet spraying machine, hoses, and nozzle to prevent clogging or malfunctions.
Pump Pressure: Ensure consistent pump pressure for uniform spray and material flow.
Would you like a checklist format or printable version for field use?
