Dynamic Cone Penetrometer (DCP) Guide
What a DCP measures
Made in Northville, Michigan since 1983
A dynamic cone penetrometer measures the strength of soil and base layers in place, without a lab. It drives a steel cone into the ground with a hammer dropped from a fixed height, and records how far the cone travels with each blow. That rate, in millimeters per blow, is the DCP index. Engineers use it to estimate the California Bearing Ratio (CBR), find where one soil layer ends and the next begins, and check that a subgrade or base course is compacted before paving. The test is set out in ASTM D6951.
Salem Tool Company has machined DCPs in our own shop in Northville, Michigan since 1983, to ASTM D6951 and U.S. Army Corps of Engineers standards, under an ISO 9001 certified quality system. All joints are threaded and welded, then machined and polished smooth, and our slide hammers are machined from 4 1/2" blank with finger grooves for grip. Salem Tool DCPs are in service with the Michigan Department of Transportation, the U.S. Air Force, the Minnesota Department of Transportation, Carlton County, Minnesota, NAVFAC, and Canada's Department of National Defence.
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How the DCP test works
1. Stand the DCP upright on the test point and seat the cone.
2. Read the starting depth on the vertical scale. Our scale guides hold it in place, so one person can run the test alone.
3. Lift the 8 kg hammer to the handle and let it fall. It drops 575 mm (22.6 in).
4. Record the penetration after each blow, or after a set number of blows in firm ground.
5. Continue to the depth you need. Our standard 37.75" drive rod tests to 36", and extension rods go deeper.
6. Remove the DCP. A reusable hardened tip comes out with the rod, and our extractor jack makes that easier in hard ground. A disposable tip stays in the ground, so the rod lifts out with far less effort.
Single mass or dual mass
Single mass: one 8 kg hammer, for firm to hard soils and base layers (CBR 10 to 100).
Dual mass: an 8 kg hammer that becomes 4.6 kg with the extra weight removed, for very soft soils through hard base (CBR 0.5 to 100). In soft ground the 8 kg hammer can drive the cone too far in one blow to give a useful reading, and the 4.6 kg setting keeps each blow measurable.
From DCP index to CBR: the U.S. Army Corps of Engineers correlation in ASTM D6951 is CBR = 292 / DCP^1.12, with DCP in millimeters per blow. The standard gives separate equations for lean clays (CL) below CBR 10 and for fat clays (CH).
Disposable or reusable cone tips
A reusable hardened tip threads onto the drive rod and comes out with it after the test. It suits occasional testing and softer ground. A disposable tip pushes onto a tip adaptor and stays in the ground, so the rod lifts out with far less effort. It suits high-volume testing and hard or rocky ground.
Every Salem Tool kit includes both, so crews can choose on site. Replacement disposable tips come in packs of 25, 100, and 250, and reusable tips come singly or in fives.
We do our best to ship your order the same day from our large inventory
Common questions
What is a dynamic cone penetrometer and how does it work?
A dynamic cone penetrometer (DCP) measures the strength of soil and base layers in place. An 8 kg hammer drops 575 mm onto an anvil and drives a 60° steel cone into the ground. The penetration per blow, in millimeters, is the DCP index: soft ground lets the cone travel further with each blow, and firm ground stops it sooner. One person can carry the kit and run a test in a few minutes.
How do you convert DCP readings to CBR?
Divide the penetration by the number of blows to get the DCP index in millimeters per blow, then apply the U.S. Army Corps of Engineers correlation in ASTM D6951: CBR = 292 ÷ DCP^1.12. A reading of 10 mm per blow works out to a CBR of about 22. ASTM D6951 gives separate equations for lean clays (CL) below CBR 10 and for fat clays (CH).
What does ASTM D6951 require for a dynamic cone penetrometer?
ASTM D6951 is the standard test method for using the DCP in shallow pavement applications. It sets an 8 kg hammer with a 575 mm drop, a replaceable 60° cone with a 20 mm base diameter, and a vertical scale for reading penetration. It also allows a 4.6 kg hammer for weak soils. Every Salem Tool kit is built to ASTM D6951 and U.S. Army Corps of Engineers standards.
Single mass or dual mass: which should I buy?
If your crews test only firm soils and base layers, a single mass kit with the 8 kg hammer covers it (CBR 10 to 100). If they also test soft subgrades, buy dual mass: the 4.6 kg setting keeps each blow short enough to measure in soft ground, so one instrument covers CBR 0.5 to 100. Compare our kits.
How much does a dynamic cone penetrometer kit cost?
Our kits run from $895 for the 4.6 kg Foundation set to $2,850 for the Dual Mass Deluxe kit. The standard Dual Mass Quick Connect kit is $2,035. Orders over $1,500 ship free with code SHIPFREE, and in-stock kits ordered by 3 PM Eastern usually ship the same day. See all dual mass kits or all single mass kits.
Can I order on a purchase order?
Yes. Request a quote with your RFQ or PO attached and we will reply within one business day, or call (248) 468-9000.