Conventional borings will be made for a planned industrial building in an area where it is known that a relatively limited thickness of soil (estimated to range between 10 ft and 25 ft deep) overlies...

Conventional borings will be made for a planned industrial building in an area where it is known that a relatively limited thickness of soil (estimated to range between 10 ft and 25 ft deep) overlies rock. For the purpose of planning excavation work for the new structure and estimating the cost, it is important that the depth of the soil overburden be defined, the zone of underlying weathered rock be defined (material that probably could be excavated with conventional digging equipment), and the depth where “sound” rock begins be determined (material excavation that will require special equipment or procedures). The standard split spoon sampler and SPT procedure will be used to obtain samples of the subsurface materials. What SPT blow-count criteria can be applied to define soil, weathered rock, and “sound” rock, and the depths where a change of material occurs?