A cone penetration test (CPT) is one of the most efficient ways to build a detailed picture of what’s happening beneath a site, without the time and disturbance of drilling a borehole at every location.
How It Works
An instrumented steel cone, mounted on a series of rods, is hydraulically pushed into the ground at a constant rate. Sensors in the cone continuously record two key measurements as it advances: tip resistance (the force needed to push the cone tip through the soil) and sleeve friction (the resistance along the cone’s shaft). A pore pressure reading (CPTu) is often added as well, giving a third data stream. Together, these are logged continuously with depth, rather than at set intervals like many other test methods.
What It Tells Engineers
From the tip resistance and friction ratio, engineers can interpret soil type and consistency down the full profile — identifying layers of sand, clay, silt or looser and denser zones — without needing to physically retrieve a sample at every change. CPT data also feeds directly into geotechnical design parameters such as soil strength, stiffness and, with pore pressure data, indicators relevant to liquefaction assessment in suitable ground conditions.
CPT vs Boreholes
CPT is generally faster and causes less ground disturbance than drilling, and because the data is continuous rather than sampled at intervals, it often picks up thin layers or transitions that a borehole log might miss between sample depths. The trade-off is that CPT doesn’t recover a physical soil sample for direct laboratory testing, so on many projects the two methods are used together — CPT to profile the site efficiently, with targeted boreholes or test pits where a physical sample is needed.
Where CPT Is Used
CPT is common on larger infrastructure, commercial and industrial projects — solar and wind farms, subdivisions, pipeline routes and multi-storey developments — where engineers need a reliable strength and stratigraphy profile across a wide site, efficiently and with minimal disruption.
Our geotechnical investigation & engineering service can scope CPT alongside other testing methods for your site.