The primary objective of DP is to determine the resistance of soils and soft rocks in situ to the dynamic penetration of a cone. A hammer of a given mass and given height of fall is used to drive the cone. The penetration resistance is defined as the number of blows required to drive the cone over a defined distance. A continuous record is provided with respect to depth, however, no samples are recovered.
The requirements for DP, according to IS EN 1997-1 and IS EN 1997-2, are specified in EN ISO 22476-2 Geotechnical Investigation and Testing – Field Testing – Part 2: Dynamic Probing. BS 5930:2015, Charles (2005) and BRE (2003) outline the strengths and limitations of DP. The system is quick, simple, relatively inexpensive and robust which allows a greater number of tests to be carried out in a day. Furthermore, access is possible to remote and awkward locations, particularly in comparison to a shell and augur rig.
The primary limitation of DP is that the soil cannot be identified; therefore, Substruck recommends a minimum of one sample for each site. The secondary limitation to this method is where occasional cobbles and boulders are incorrectly interpreted as bedrock, particularly in glacial material.
The test results of EN ISO 22476-2 are specially suited for the qualitative determination of a soil profile together with direct investigations (e.g. sampling according to EN ISO 22475-1), or as a relative comparison of other in situ tests. These results may also be used for the determination of the strength and deformation properties of soils, generally of the cohesionless type but also possibly in fine-grained soils, through appropriate correlations. The results can also be used to determine the depth of very dense ground layers e.g. to determine the length of end bearing piles, and to detect very loose, voided, back-filled or in-filled ground. Penetration resistance can give an indication of the density index of coarse soil and the undrained shear strength of fine soils.
Dynamic probing is distinguished in Table 1 of EN ISO 22476-2, based on the dimensions and masses of the components of the driving device. DPH is selected for general use as giving a good compromise between sensitivity in loose materials and penetration rates in denser materials, however, there has been far more research completed on DPSH. Please feel free to contact the team here at Substruck to learn more about dynamic probing. We will be happy to discuss your requirements further and determine the most appropriate approach for your project.