Taking A Look At Cone Penetration Testing (CPT)

by | Jan 22, 2021

CPT is one of the most common geotechnical investigation methods available. If you’re looking for a reliable, versatile and efficient way of sampling ground conditions. There are several types, however, and the method carried out by your contractor will depend on various factors. The team here at Borehole Solutions, who offer an extensive CPT service, wanted to explain the process in a little more detail.


How Does It Work?

Before we go any further, it’s worth understanding how exactly cone penetration testing works. Developed initially by the Dutch, CPT involves pushing a cone with sensors attached downwards into the ground. The cone is pushed down using one of a variety of different rigs, either a crawler-mounted rig, industry-specific trucks or semi-tracked machinery. This drilling down is carried out at a predetermined controlled rate and various measurements can be obtained. These include:


Bearing Capacity

Calculating bearing capacity is what cone penetration testing was originally invented for. In a nutshell, it helps determine how much weight the soil below can take, or ‘bear’, before failing structurally.


Cohesive Soil Strength

It’s perhaps easier to think of soil cohesion in another way, and that’s how easily it sticks or clumps together! The more cohesive the soil, the more stable it is (generally). To find out more about soil cohesion, read our previous blog post, here!


Pore Water Pressure Data

By calculating pore water pressure (pwp) data – the amount of pressure of groundwater within rock – geotechnical engineers can then calculate the “stress state” of the ground they’re testing. To gather this data, a particular type of cone called a piezometer is used.


Soil Liquefaction Analysis

Without getting too technical, CPT testing can be used to help detect the velocities of both longitudinal and shear waves (the kinds of seismic waves generated by earthquakes, for instance) which in turn can be used to help determine how likely soil is to liquefy.

Liquefaction is when soil loses its structural strength and begins to behave, as the name might suggest, like a liquid. If ever you’ve seen images of buildings seeming to have sunk into the ground following a major earthquake, that’s generally as a result of the soil beneath liquefying and giving way.


UXO (Unexploded Ordnance)

Though not often tested for outright, the cone (specifically a piezocone) can be fitted with a magnetometer. This enables the detection of any potentially lethal unexploded materials (by sensing large magnetic materials) thus making CPT one of the safest sampling methods, as well.

Basically, what all the sets of data give geotechnical engineers is a better picture of the soil beneath them. With CPT, you’re able to determine suitability for processes ranging from excavation to all the way through to an inspection of a building’s existing foundations. The more comprehensive an understanding you have of that ground, the more confident you can be with consequent decisions; whether to proceed to build or not, for instance, or whether remedial work/structural repairs potentially need to be carried out on existing properties.


Why CPT?

Many contractors opt for cone penetration testing (CPT) over standard penetration testing (SPT) – but why? Well, the answer’s pretty simple; in terms of accuracy, cost-effectiveness and the nature of the soil profile it returns, CPT almost always comes out on top.


Contact Us For CPT Services

So, if you’d like to find out more about our CPT services, then get in touch! Contact Borehole Solutions today on 01733 200 501 or by emailing us at info@boreholesolutions.com.