Site Setup, Ground Conditions, and Outrigger/Stability Considerations
Ground bearing and level
OSHA 1926.1402 requires firm, drained, and graded ground, with supporting materials sized so the manufacturer's leveling and support specifications are met. Outrigger floats spread a concentrated reaction over an area; ground bearing pressure = reaction ÷ mat area. Compare that to the soil's allowable bearing capacity and add margin for dynamic loads, rain, and backfill. Never assume a mat is adequate because it looks big.
Setup rules
Fully extend outriggers and use the manufacturer's floats or mats. Do not use the outrigger beam as a jack. Keep outriggers away from excavations, utility vaults, septic tanks, and buried lines. Maintain the manufacturer's level tolerance, commonly 1% or less. Check swing clearance, tail swing, and boom clearance before lifting. On crawlers, the track bearing area and ground pressure matter; on rubber, tire capacity and suspension affect stability.
Worked example
An outrigger reaction is 72,000 lb. A 3 ft × 4 ft mat gives 12 ft², so pressure is 6,000 lb/ft². If the soil is good for 3,000 lb/ft², the required area is 72,000 ÷ 3,000 = 24 ft². Use a 4 ft × 6 ft mat. Also check the mat's crushing strength and the float's own rating.
Traps
Using the crane's total weight instead of the outrigger reaction; ignoring dynamic and wind loads; placing mats over a backfilled trench; short-jacking outriggers; and setting up on a slope because 'the chart still says 100 percent' are classic errors.