Dynamic Cone Penetrometer (DCP) Testing
A Dynamic Cone Penetrometer (DCP) test gives you a fast, portable read on soil strength at depth, without the setup time of a full CBR or plate bearing test. At Site Testing Services (National) Ltd, we use DCP testing to profile subgrade and subbase strength across multiple points on a site, quickly and to the standards your project needs.
What is a Dynamic Cone Penetrometer test?
A DCP test uses a steel cone, driven into the ground by a sliding hammer of standard mass falling a fixed height, to measure how far the cone penetrates the soil with each blow. The penetration rate per blow is recorded down through the ground, giving a continuous strength profile rather than a single reading at one depth.
Standard DCP testing reaches 800mm below the test start point. Where a deeper profile is needed, an extension rod takes the test down to 1,500mm. Because the kit is man-portable and needs no reaction load or heavy plant to run, unlike a plate bearing test, we can test at far more points across a site than would be practical otherwise. That is what makes DCP useful for infill data between existing test locations or boreholes.
How does a DCP test work?
The test works by converting blow counts into an equivalent CBR value. As the cone is driven in, we record the penetration achieved for each hammer blow. Where the penetration rate changes, that marks a boundary between pavement or subgrade layers of different strength, so the test also tells you layer thicknesses, not just a single strength figure.
The correlation between penetration rate and CBR value used in the UK was developed by TRL (the Transport Research Laboratory) and is the same correlation referenced in National Highways’ CS 229 guidance for pavement investigation. We apply that established relationship to convert your site’s raw penetration data into a CBR profile your design team can use.
DCP Test Procedure
Test Location & Preparation
We record the test start depth relative to ground level, along with the DCP offset, the zero reading taken before driving begins, and site conditions such as weather. A check of the cone diameter is carried out and confirmed before every single test, since a worn or incorrect cone will skew the results.
Equipment
The kit consists of a drive rod with a replaceable conical tip (60 degree apex angle, 20mm diameter), an 8kg sliding hammer with a fixed 575mm drop height, and a graduated scale to record penetration. An extension rod is added where testing needs to go beyond 800mm.
Driving & Recording
The hammer is dropped repeatedly from its fixed height, and we record the cumulative penetration after each blow. This continues down through the profile, at multiple locations across the site, to build a picture of strength with depth across the area you need tested.
Data & Reporting
The blow-by-blow penetration data is converted into an equivalent CBR profile and plotted against depth, with layer boundaries identified where the strength changes. You get a clear profile you can hand straight to your design engineer, usually the same day.
DCP vs CBR Test vs Plate Bearing Test: Which Do You Need?
All three tests tell you something about ground strength, but they answer different questions and suit different situations.
| Test | Speed | Coverage | Output | Best used for |
| DCP | Fast, minutes per point | Many points across a site | Equivalent CBR profile with depth | Infill data, restricted-access areas, quick multi-point checks |
| CBR Test | Moderate | Fixed test locations | Measured CBR value at each location | Design-stage bearing capacity for pavement and foundation design |
| Plate Bearing Test | Slower, needs kentledge | Fixed test locations | Load-settlement relationship, bearing capacity | Crane pads, piling mats, working platforms, verifying real loaded response |
If you need a definitive, specified CBR value for a design calculation, or a real loaded response for a crane pad or piling mat, our CBR Test or Plate Bearing Test services are the right choice. If you need to check strength consistency across a wider area, get infill data between existing test points, or test somewhere a full rig cannot easily reach, DCP is usually the more practical option. Our team can advise on the right combination for your project when you get in touch.
Applications
- Assessing subbase, capping, and formation strength for road and pavement construction
- Providing infill data between existing boreholes or CBR test locations
- Checking verges, embankments, and other areas with restricted access
- Quality control of compacted fill during earthworks
- Quick strength checks ahead of a more detailed CBR or plate bearing test, where one is needed
Standards and Accreditation
Unlike CBR testing, which is carried out to BS 1377, DCP testing does not have a single UK accredited standard body method. It is generally documented and delivered as an in-house method, run against the TRL Dynamic Cone Penetrometer method, the same protocol referenced in National Highways’ CS 229, Data for pavement assessment. The depth and correlation figures we work to are set out in TRL’s own technical guidance on DCP tests and analysis.
This means a DCP result is best used as a fast, reliable indicator of strength and consistency across a site, rather than as a like-for-like replacement for a BS 1377 CBR value where one is specifically required.
Why Choose STS for DCP Testing?
Our engineers carry out DCP testing across England and Wales, with same-day data so your design team is not left waiting. Because we also deliver CBR testing and plate bearing tests, we can advise honestly on which method (or combination of methods) actually suits your site, rather than defaulting to whichever test we happen to be offering. Where lab verification would add value alongside a DCP profile, our UKAS-accredited Laboratory Testing service can confirm results from the same site visit.
Frequently Asked Questions
What is a DCP test? A Dynamic Cone Penetrometer test measures soil strength at depth by recording how far a steel cone penetrates the ground with each blow of a standard sliding hammer, giving a continuous strength profile rather than a single reading.
How does a DCP test differ from a CBR test? A CBR test measures bearing ratio directly at a fixed test location to BS 1377. A DCP test estimates an equivalent CBR value from penetration data using an established TRL correlation, and can be run at many more points, more quickly, across a wider area.
Is a DCP result accepted by Building Control or design engineers? For general profiling, consistency checks, and infill data, yes. Where a specification calls for a BS 1377 CBR value specifically, a full CBR test is usually required instead, since DCP has no equivalent accredited standard.
How deep can a DCP test go? Standard testing reaches 800mm below the start depth. With an extension rod fitted, this extends to 1,500mm.
How long does a DCP test take? Each test point takes a matter of minutes, which is what makes DCP practical for testing many locations across a site in a single visit.
Can a DCP test replace a full CBR test? Not where a specified CBR value is required for design. DCP is best used alongside CBR testing, for infill data, wider-area profiling, or sites where full CBR testing is impractical.
[H2] Get in touch
Call Site Testing Services (National) Ltd on 0330 6339 988 to discuss your project and get a free quote for DCP testing anywhere in England and Wales.
