Guide to CPT (cone penetration testing)

In-situ soil testing

Cone penetration testing takes place in-situ, with virtually instantaneous results.

A cone penetrometer is pushed vertically from a rig into the ground at a constant rate of penetration of 20mm per second (schematic at bottom of page).

During penetration, measurements are made of the cone resistance, the side friction against the cylindrical shaft and, in piezocone tests, the pore water pressure generated at penetration by the cone.

The measurements are made and recorded using electrical devices, the frequency of the readings provides a detailed picture of the variation of the measured parameters with penetration depth.  Depths of up to 100m can be reached. At present Lankelma has a repetoire of 17 cones for different site investigations.

see some completed projects

Multiple and simultaneous readings The ability of the CPT to collect multiple and simultaneous readings, with depth, is a valuable asset. Special cones can be run concurrently with the standard cone test to evaluate the natural foundation material properties which include : shear wave velocity in-situ water content porewater pressure shear modulus shear strength

Purpose of CPT To determine sub-surface stratigraphy and identify materials present To estimate geotechnical parameters To provide results for direct geotechnical design Advantages of CPT Greater delineation of strata since readings are taken every 2cm Repeatable, reliable penetration details High quality, real time results Using the instant CPT results, engineers can select, on site, the best locations for sampling, dissipations tests etc. Minimal soil disturbance >> High productivity (up to 150m tested per day) CPT platform can be used for deploying high quality push fixed piston samplers >> More manageable data handling Disadvantage Cone penetration testing cannot be carried out through rock layers.