Structure Designing

They're very different tests created for very different reasons. You can correlate some of the same values out of them, but the problems they were invented to solve are different. CBR is a pretty old test and it's very targeted at gravels and their reaction to bearing near the surface of the ground. SPT is a dynamic test that is focused at developing a strength log through a depth. They might be interchangeable for a certain goal, or they might not be.

You probably want more depth information for a building, which is why CBR isn't really that helpful. If you're doing quality control on a road you might not. Realistically, though, I think road construction uses DCP a lot now.

SPT isn't necessarily the thing you'd use for building construction though. There are lots of investigations you might use depending on the soil conditions, local practice and what the building foundation system is expected to be.

The following excepts copy -paste ( SPT from BOWLES , CBR from WEB );



California Bearing Ratio (CBR) is a material property , a measure of the bearing strength of a pavement layer and does not change with compaction , consolidation while SPT varies also with relative density level.

The CBR value of crashed stone aggregate is assumed to be 100% .










I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

If memory serves, a true CBR is obtained by putting your aggregate in a drum and spinning/pulverizing it for a given time. It's an aggregate durability measurement. The SPT is a different animal all together. Both of them give you some idea of the soil you are dealing with, but they test different things.