Site and Job Planning, Setup, and Ground Conditions
Site and Job Planning, Setup, and Ground Conditions
This domain tests whether you can pick and prepare a setup that will not sink, shift, or tip once the boom swings out and the hopper is full. Most questions reduce to one idea: the load path from boom tip to soil must be continuous, verified, and inside the manufacturer's limits.
Size the pads; do not guess
- The loaded outrigger carries far more than an axle reading - machine weight, boom weight, and concrete in the line all shift to one corner.
- Ground bearing pressure = load ÷ effective pad area. Size for the weakest soil you will actually sit on; uncompacted backfill, frost, and buried vaults are not "firm ground."
- Manufacturer slope limits, mat size, and outrigger extension are limits, not suggestions. Never crib a partly extended outrigger to make a tight spot work.
- Check up as well as down: power lines, bridges, tree limbs. Call 811 before setting up over anything buried.
Worked example
A rear outrigger is expected to carry 24,000 lb; the soil is rated at 2,000 psf. Required area = 24,000 ÷ 2,000 = 12 ft². A 3 ft × 3 ft pad (9 ft²) gives 2,667 psf and fails. A 3.5 ft × 3.5 ft pad (12.25 ft²) gives 1,959 psf - passing with no margin - so choose a 4 ft × 4 ft pad: 16 ft², 1,500 psf, leaving working margin for boom swing and a wet load.
Traps that cost marks
Using axle or total-weight numbers instead of the outrigger reaction; setting one corner on a pad and three on bare dirt; trusting that the ground held for a lighter pump last week; setting outriggers beside an excavation without accounting for its depth; ignoring the slope limit because the bubble "looked close."