Safety Sense

Outriggers shall be used according to the manufacturers’ specifications or design data, which shall be available. Floats, when used, shall be securely attached to the outriggers.
Wood blocks or other support shall be of sufficient size to support the outrigger, free of defects that may affect safety and of sufficient width and length to prevent the crane from shifting or toppling under load.

Soil Compaction

If the soil type or amount of compaction is unknown:

  • Sometimes soil analysis is available from the contractor, but not often.
  • If it remains unknown, take your best guess. Get enough cribbing for your guess, then test the soil by SLOWLY bringing the boom over the outriggers. ┬áIf the outrigger begins to sink, QUICKLY retract the boom, then increase the cribbing. Keep testing until the outriggers no longer sink. Check for sinking repeatedly during the pour.

Examples of the Load Capacities of Various Soil Types

Soil Type Load Bearing Capacity
Virgin Ground 22 PSI
Asphalt 29 PSI
Compressed crushed stone 36 PSI
Clay/Silt soil, firm 43 PSI
Mixed granular soil 51 PSI
Firm compacted gravel 58 PSI
Firm compacted gravel (more compacted) 72 PSI
Firm compacted gravel (more compacted, class 5) 109 PSI
Brittle weathered rock 145 PSI
Concrete (unknown mix) 1000 PSI