Soil formation and nature

Soils in the engineering sense are either naturally occurring or man-made. They are distinguished from rocks because the individual particles are not sufficiently bonded together. These include the surplus and residues from construction processes such as excavation spoil and demolition rubble, from industrial processes such as ashes, slag, pulverised fuel ash (PFA), mining spoil, quarry waste, industrial by-products and from domestic waste in landfill sites. They can be detrimental to new works through being soluble, chemically reactive, contaminated, hazardous, toxic, polluting, combustible, gas generating, swelling, compressible, collapsible or degradable. All waste materials should be treated as suspect because of the likelihood of extreme variability and compressibility (BRE Digest 427: Part 1).These deposits have usually been randomly dumped and any structures placed on them will suffer differential settlements.