Crane Mats & Outrigger Pads
A crane that sinks or tips because the ground gave way is one of the most common causes of crane accidents. Mats and pads spread the load over more soil so the ground can carry it. They are not accessories; they are part of the lift.
- Crane Operators
- Riggers
- Lift Directors
Why they matter
- Outrigger floats or crawler tracks concentrate thousands of pounds on a small area. Soft or wet ground can crush or shift.
- OSHA requires the controlling contractor to ensure ground conditions are firm, drained and graded enough to support the equipment, and the equipment must be level (1926.1402).
- The operator must verify that the crane is level and the support is adequate before lifting. See Crane Setup.
Know the numbers
- Find the crane's maximum outrigger or track load in the manual or load chart. Add the weight of the load and equipment.
- Ground bearing pressure equals load divided by the contact area. Soil has a limit (allowable bearing pressure) that depends on type and moisture. Ask an engineer or geotechnical report. See Geotechnical Reports and Soil Classification.
- Size the mat so the pressure under it stays below the ground limit, with a safety margin. A larger mat reduces pressure.
Types
- Timber mats made of stacked or bolted hardwood, common on construction sites.
- Composite or plastic mats that are light, long-lasting and do not absorb water.
- Steel plates and aluminum mats for heavy loads.
- Outrigger pads or floats sized to the crane.
- Cribbing stacked in a crisscross pattern to build up uneven ground or to support the float over a void.
Placement
- Prepare the ground: remove loose soil, level it and compact it where practical
- Place mats on firm ground and cover the whole outrigger float or the track area, with equal support underneath
- Do not span a void with a mat unless designed for it. Check for pipes, trenches, tanks and backfill
- Keep mat stacks level and stable; use full contact, no gaps or hollows
- Watch for rain, thaw, leaks and vibration, which weaken soil during the day
- Inspect mats for cracks, rot and damage before use; replace damaged ones
- Monitor the crane during the lift for settling or tilt and stop if it moves
Standards & references
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