SPT, DCP and MDD: choosing the right soil test for the question
SPT, DCP and MDD are often grouped together as soil tests, but they answer different engineering questions. A useful test programme begins with the decision the project team needs to make, then selects the method that produces relevant evidence.
SPT: resistance at borehole depth
The Standard Penetration Test is carried out in a borehole and records the blows needed to drive a standard sampler. Results support interpretation of subsurface consistency or density and can inform foundation assessment when considered with the soil description, samples and local engineering judgement.
DCP: a rapid profile near the surface
The Dynamic Cone Penetrometer records penetration under repeated hammer blows. It is useful for profiling changes in near-surface strength and checking pavement or earthwork conditions across several locations. It does not replace a borehole where deeper geology, groundwater or samples are required.
MDD: a compaction reference
Maximum Dry Density testing establishes the relationship between moisture content and achievable dry density for a material under a specified compactive effort. Site density results can then be compared with that laboratory reference to verify whether placed fill meets the project requirement.