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.
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. If 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|
|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|