Static cone penetration test, CPT, (ASTM D3441)

Static cone penetration test, CPT, (ASTM D3441):

This is also known as Dutch cone test the reason behind that is, the mechanical CPT was originally developed in Netherland, but with the passage of time their was a evolution and the many new cones were invented, now a days electric cone and piezo cone are world widely used.

In the simplest form of this test a cone of base area 10 cm2 with base dia. 3.57 cm and apex angle 60 degrees is pushed into the ground at a rate of 10 mm per sec. to 20 mm per sec (ASTM D3441). Just above the cone a friction sleeve of area 150 cm2 is located. Data is collected which includes the cone resistance Qc and the sleeve resistance Qf. These two factors are very important they are used in design. Cone resistance and sleeve resistance are used in computing friction ratio.

Correlations:

Like SPT correlations have also been developed for the CPT. These correlations are between the bearing capacity, strength and sensitivity of clay, relative density of sand and over consolidation with SPT values and the pile design parameters. These correlations help u a lot in understanding the cone penetration tests.

Conventional borings can partially be replaced and instead of them we can use CPTs. The operation is quite speedy and therefore considerably large amount of data is obtained in a very short time. It is a very simple test and is very suitable for soft clays and normally suitable to the medium coarse sands. One of the major draw back of this method is that there is no recoverability of the sample once operated so it cannot be further identified and classified, which results in the difficulty and problem in advancing the cone to denser or to harder deposits.