Building Question - MOT road stone

[BIG MAC]

Soil mechanics etc will determine bearing capacity using a dynamic probe. The reason for sub base is to provide a reliable medium to transmit loads from the structure down into good bearing strata. I will often use crushed road planings from demolition companies for this as they compact very well. Granular fill is often used to make a 'contained formation' inside already cast footings and retaining walls, sometimes even above a raft to permit the casting of a higher level slab. Granular material particularly riverwash stone will tend to  'self compact' under its own weight.