We have over 45 years’ experience utilising dynamic probing and penetrometer testing as part of a site investigation for characterising the strength of the ground and for the location of: solution features, areas of made ground, soft deposits, tunnels and other underground voids and cavities. The tests are based on BS EN ISO 22476-2: 2005 specifications.
A dynamic probing test (DPT) involves driving a cylindrical sacrificial or fixed cone into the ground using a high frequency percussive hammer. The cone is attached to a 1m section steel rod with a nominal diameter of approximately 35mm and graduation markings set at 100mm intervals. Depending upon the chosen method, the drop height can be adjusted.
Blows per 100mm are recorded and after every 1m section a torque reading is recorded. A further rod is then added and the process is continued until the probe refuses to penetrate the ground or the test reaches the required depth.
The results from this method can be correlated directly to a standard penetration test ‘N’ value. The results are plotted on a graph, providing a visual interpretation of the different soil strata encountered.
Three types of DPT are available: A DPSH test in which a 63.5kg weight is dropped 750mm; a DPH test in which a 50kg weight is dropped 500mm and a lightweight DPL test in which a 10kg weight is dropped through 500mm.
Rubber tracked or wheeled site investigation rigs are used; they have a width of approx 850mm and require a level working space of about 3m x 2m and minimum headroom of 2.8m. Handheld equipment is used for the DPL test on sites where rig access is problematic.
Results (blows vs depth) are plotted until the required depth has been achieved or at refusal (3 x 30 blows or 1 x 50 blows).