ASTM D6951: the dynamic cone penetrometer standard

ASTM D6951/D6951M is the ASTM test method for using the dynamic cone penetrometer (DCP) in shallow pavement work. It measures how far an 8 kg hammer drives a steel cone into soil or compacted material with each blow, and relates that penetration rate to in-place strength, such as an estimated CBR. The current edition is D6951/D6951M-18, reapproved in 2023.

What the standard covers

Hammer: 8 kg (17.6 lb). An optional 4.6 kg (10.1 lb) hammer is allowed where the 8 kg hammer sinks too far in soft ground.
Drop: 575 mm (22.6 in).
Cone: 20 mm diameter, 60° point.
Result: penetration rate, in millimeters per blow (the DCP index).
Typical depth: down to 1,000 mm (39 in).
Materials: undisturbed soil, compacted fill, granular base, and weakly stabilized or modified materials.
Typical work: pavements and floor slabs, with the instrument held vertical.

What engineers use it for

Estimating CBR in place. The penetration rate converts to an estimated in-situ CBR. See DCP to CBR for the formula and a table.
Finding layer thickness. A change in penetration rate marks the boundary between layers.
Indicating shear strength of each layer.
Finding soft spots. In fairly uniform material, penetration rate can be related to density. The DCP does not measure density directly.

Where the method doesn’t apply

Highly stabilized or cemented materials.
Granular material with a large share of aggregate over 50 mm (2 in).
Material under a bound or highly stabilized layer, unless an access hole is drilled or cored through it first.

Drive rod extensions let the DCP test deeper, but they add mass, inertia and friction along the rod. The standard notes that correlations apply only to the configuration they were developed for.

A field CBR, not a lab CBR

The standard says a DCP gives a field or in-situ CBR, which usually won’t match a laboratory or soaked CBR of the same material. Compare DCP results against field values.

Other DCPs and other standards

ASTM D6951: 8 kg DCP, 575 mm drop, 20 mm 60° cone. Pavement layers and subgrade, from the surface down.
ASTM D7380: 2.3 kg (5 lb) DCP, 20 in drop. Compaction checks in trenches and confined backfill at shallow depth.
Sowers DCP: 15 lb mass, 1.5 in 45° cone, correlated to the SPT. Testing at the bottom of a hand-augered hole, 15 to 20 ft down.

Each instrument has its own correlations. A specification that calls for DCP testing to ASTM D6951 means the 8 kg instrument. More on the Sowers DCP in the DCP Guide.

Salem Tool kits and ASTM D6951

Salem Tool builds its DCP kits in Northville, Michigan, to ASTM D6951 and U.S. Army Corps of Engineers standards.

Single mass DCP kits: 8 kg hammer, CBR 10 to 100.
Dual mass DCP kits: 8 kg and 4.6 kg hammers, CBR 0.5 to 100.

Compare the kits, or request a quote for a purchase order.

Common questions

What is ASTM D6951?

ASTM D6951/D6951M is the standard test method for using the dynamic cone penetrometer in shallow pavement applications. It measures the penetration rate of an 8 kg hammer DCP through soil and compacted materials and relates it to in-place strength, such as an estimated CBR.

What hammer weight does ASTM D6951 use?

An 8 kg (17.6 lb) hammer dropped 575 mm. The standard allows an optional 4.6 kg (10.1 lb) hammer where the 8 kg hammer penetrates too far in soft ground. A dual mass kit carries both.

Does ASTM D6951 measure soil density?

No. In fairly uniform material, penetration rate can be related to density to find soft spots, but the DCP does not measure density directly.