Dynamic Cone Penetrometer (DCP)
Testing to establish CBR profiles up to 1m depth using a DCP
The Dynamic Cone Penetrometer (DCP) is an instrument designed for the rapid in-situ measurement of the structural properties of existing road pavements constructed of unbound materials. The robust and simple design means that the DCP is quick and easy to use, portable, and suitable for use in locations where access may be difficult. It is commonly used to determine a California Bearing Ratio (CBR) profile for pavement design.
DCP testing consists of using the DCP’s free-falling hammer to strike a metal cone, causing the cone to penetrate the base or subgrade soil, and then measuring the penetration per blow, also called the penetration rate (PR), in mm/blow. This measurement denotes the stiffness of the tested material, with a smaller PR number indicating a stiffer material. In other words, the PR is a measurement of the penetrability of the subgrade soil.
Correlations to CBR in homogenous, fine grained soil types are potentially the best use of the tool, or for finding boundaries of known (engineered or natural) layers where there is significant difference in resistance i.e. soft clay over dense gravel. Heterogenous soil types, e.g. made ground are not suitable for DCP testing.
Limitations of this test
Whist it's quick and easy it provides only an approximate assessment of CBR
As the device is ground penetrating a full utilities survey is required beforehand
Great for tight spaces
Minimal access required but should only be selected when no other method is viable