Ground bearing capacity
Also called Allowable bearing pressure
The maximum bearing pressure the ground can safely support without excessive settlement or failure, established through site investigation and geotechnical assessment. It varies significantly with soil type, moisture content and previous ground disturbance, and is the key figure used to size crane mats and outrigger pads.
In practice
There is no default value, and a figure taken from a textbook row for “firm clay” describes a soil class rather than the ground you are standing on — after a wet fortnight, after a service trench has been backfilled, after plant has churned the surface. Where a lift is planned against an assumed capacity, the assumption belongs in the lift plan in writing, and the value that may be used is the temporary works designer’s decision.
Where this comes from: UK ground investigation and lift planning practice. The allowable figure for a given site comes from a geotechnical assessment of that site, not from a published table.
Where it matters on site
This is the figure most often missing when a hire desk is asked to size a mat. We can size for a stated allowable pressure; we cannot supply the pressure itself. If nobody on the project can name it, the honest next step is a ground investigation or an engineered working platform — not a larger mat chosen by feel, which changes the applied pressure without telling anyone what it has to be below.