Ground bearing pressure and crane mats explained
A crane is only as safe as the ground under its outriggers. A guide to ground bearing pressure, why soft ground fails a lift, and how crane mats spread the load to keep it stable.
7 min read · 2026-07-04
A crane concentrates an enormous load onto a few small outrigger pads. If the ground beneath them cannot take that pressure, the pad sinks, the crane lists, the radius changes and the lift is lost in seconds. More lifting incidents trace back to the ground than to the crane itself. Getting the ground right is not a detail, it is half the lift.
The good news is that ground is predictable. The load under each outrigger can be calculated, the ground capacity can be assessed, and mats can be sized to bridge the gap. None of it is guesswork once the numbers are done, which is exactly what a ground assessment in the lift study is for.
The ground is part of the crane
An outrigger pad puts huge pressure on a small area. The lift is only safe if the ground under every pad can carry that pressure with a margin.
Why soft ground fails a lift
Outrigger pads are small, so even a moderate load creates very high pressure beneath them. Ground that looks firm enough to walk on, or to park a truck, can be nowhere near strong enough to take a loaded outrigger. Made ground, recently backfilled trenches, and ground over buried services are the classic traps, because the surface hides what is underneath.
Ground bearing pressure explained
Ground bearing pressure is simply the load under an outrigger divided by the area it acts on. Different ground types carry very different pressures before they fail. The chart below gives an indicative sense of how much more good ground carries than poor ground. The actual figures come from a site assessment, never an assumption.
How crane mats spread the load
A crane mat sits under the outrigger and spreads its load over a much larger area, lowering the pressure on the ground to something it can carry. The softer the ground or the heavier the load, the bigger the mat needed. Sizing the mat is the same calculation as the bearing check, run the other way: how much area does this load need to stay within the ground's safe pressure.
Pad
tiny area, huge pressure
Mat
spreads load, cuts pressure
Soft
ground needs bigger mats
Calc
not a guess, a number
The surface lies
Ground that holds a truck can still fail under an outrigger. Backfilled trenches and ground over services are the common traps. Assess what is under the surface, not just what you can see.
Every lift we plan includes a ground assessment and the right mats sized to the outrigger loads, so the crane stands on ground that holds. Tell us the load and the site and we will check the ground before the crane arrives.
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