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Dynamic Cone Penetrometer: An Essential Tool for Deep Lift® Jobs

Posted by Joel Bryant on Sep 17, 2020 10:00:00 AM

Banner - Dynamic Cone Penetrometer An Essential Tool for Deep Lift Jobs

As a consultant on many deep soil geotech jobs over the years, I have found myself recommending one critical piece of equipment repeatedly: The Dynamic Cone Penetrometer (aka the DCP). I highly recommend this tool as an essential part of your Deep Lift® rig set up. As Jim Spiegel explained in his blog post on this subject, this device is used to measure the strength of subgrade soils, and can be utilized to identify weak layers of soil within a soil mass. As you can see in the video below, a hydraulic pump drops a 30kg (60lb) hammer, driving the measuring rod into the ground.

To measure soil strength, the operator counts the number of blows it takes to drive the steel rod in 10-centimeter increments. Good soil requires 10+ blows to drive the rod 10 centimeters. Anything less is typically indicative of weak soil conditions.

DCP testing is a widely accepted means of in situ testing. Due to the common acceptance of DCP testing, many municipalities and agencies are willing to pay for this service.

Here is a hypothetical scenario for DCP use:

Soil strength data is needed under a concrete parking lot before a Deep Lift® job. Multiple tests would be performed, spread out evenly over the area. For thorough testing, each DCP test would be executed to a minimum depth of 15 – 20 feet or refusal (when the hammer blows no longer cause movement.) The test results can then be compared and analyzed to find where potential weak soil conditions may be present. This allows for accurate and effective application of the polymer to address the weak layers.

DCP testing can also be utilized prior to bidding any Deep Lift® job to develop effective injection plans, as well as accurately estimate material usage on projects. With that said, it’s not always possible or practical to perform pre-bid testing. When pre-bid testing is not performed, it would still prove highly beneficial to perform DCP testing prior to injection. I have personally encountered many situations where injection plans have been drastically altered after test results were analyzed (injection depth was added or subtracted, the weakest layers were identified, etc.) The Dynamic Cone Penetrometer is a portable tool which can easily be used in many locations where other testing methods are not feasible and it provides valuable insight into the soil conditions that need to be improved.

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Topics: Equipment & Accessories, All Posts, Lift Slabs, Deep Lift