CONE PENETRATION TEST (CPT)

The cone penetration test (CPT) is an in situ testing method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils. Based on this history it has also been called the "Dutch cone test". Today, the CPT is one of the most used and accepted in situ test methods for soil investigation worldwide.

SETUP

The test method consists of pushing an instrumented cone, with the tip facing down, into the ground at a controlled rate (usually 2 centimeters/second). The resolution of the CPT in delineating stratigraphic layers is related to the size of the cone tip, with typical cone tips having a cross-sectional area of either 10 or 15 cm², corresponding to diameters of 3.6 and 4.4 cm.

TYPE OF DATAThe 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

TEST STANDARDS

BS 1377-7:1990 ASTM D3441 - 05 Standard Test Method for Mechanical Cone Penetration Tests of

Soil ASTM D5778 - 07 Standard Test Method for Electronic Friction Cone and Piezocone

Penetration Testing of Soils

ADVANTAGES

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

DISADVANTAGES Inability to penetrate through gravels and cobbles Newer technology = less populated database than SPT Lack of sampling