Site preparation, crane positioning and ground conditions
Ground and position
Ground conditions are a leading cause of crane incidents. Before positioning, assess the ground: bearing capacity, slope, voids, underground services, recent fill, and the effect of rain. Outriggers must be fully extended unless the chart allows otherwise, and must bear on competent ground with pads or mats sized to spread the load. The outrigger load can be much greater than the load being lifted, especially when the boom is over a corner.
Position the crane so the lift path is clear, the swing radius is controlled, and the crane is level. Check clearances to buildings, powerlines and other plant. Establish exclusion zones and barricades. Confirm the crane's configuration matches the load chart: outrigger spread, counterweight, boom length and jib. Where ground is doubtful, use a competent person to assess it, or use mats, steel plates or a larger pad.
Traps in exam questions
- Positioning with outriggers on a slope, on soft fill, or over a drain or service pit.
- Using timber that is too small or too soft; pads must spread load, not just cushion.
- Forgetting that outrigger loads can exceed the lifted load.
- Ignoring wind exposure on a large sail-area load.
- Failing to check for powerlines and the required clearance.
Worked example
Rule of thumb: outrigger pads should be at least three times the area of the outrigger float and be stiff enough to spread load. If the ground is soft, use a larger pad or relocate - do not simply add more timber of unknown strength.
Exam tip
If a stem mentions soft ground, the answer usually involves relocating, matting or a competent assessment, never 'lift quickly'.