Frequently Asked Questions
Estimated 3-year maintenance cost of owning a DCP:
- Unit is calibrated by the manufacturer. No further calibration is required.
- There is a one-year warranty on all parts, provided they are used in the manner prescribed in the User’s Manual.
- Upper and Lower Rods—The DCP is an impact instrument and its longevity is a function of the number of times it is used, the soil conditions, and the operator’s technique. Lower rods have failed at the weld below the anvil (4218 Models) because of fatigue, but most often because of abuse.
- The Upper and Lower Rod on K-100 Models (with a quick connect pin) are more durable and last longer. This model uses stronger stainless steel rods and does not have a welded point at the anvil.
- When used as recommended, the Kessler DCPs have lasted for years. For almost 20 years now of manufacturing the DCP, we are delighted to report that only a few are no longer in service.
Bearing Capacity (psi) q = 3.794*CBR0.664
The “N” value is determined from the STP (Standard Penetration Test). That test is widely used for deep foundation work. A drill rig is used to drop a 140 lb hammer driving a split spoon sampler. The N value can then be used to determine the bearing capacity in psf (pounds per square foot).
Because many of the foundation equations used by engineers use the “N” value we have had similar requests for a correlation from the DCP penetration rate to the “N” value. I have surfaced this with the Corps of Engineers (who own the patent for our DCP) and they (Jeb Tingle PhD, P.E. overseer of the DCP technology) has said because they have provided a correlation to psf there is no need to have a correlation to the “N” value. If however someone wants to pay them to do the research to get a correlation from the DCP penetration rate to the “N” value, they would take this project on.
By the way, we sell the Sower’s DCP which does have a correlation from the penetration rate to an N value. Developed years ago by George Sowers at Georgia Tech for Piedmont Soils, it is very popular but much more difficult to use than our K100 DCPs. One must auger to the depth to be tested and then drive the point down 2 inches. This process can be repeated to a depth of about 11 feet.
However, the general “rule of thumb” is that if you can penetrate below the frost line, your readings will be accurate. In areas affected by frost, readings will typically be higher.