Dynamic cone penetrometer is a portable instrument that can be used to evaluate various layers of pavement such as unbound granular bases, sub-bases, sub-grades and congested narrow trenches of pipeline where testing with other instruments is difficult And it’s not possible. Cost, space and time constraints. Due to this, DCPT has gained popularity in many parts of the world.

The basic principle involved in the operation of this instrument is to measure the resistance offered by the pavement layers to the penetration of a standard cone with a diameter of 20 mm (60 in).0 Top angle) driven by a freely falling 8 kg hammer through a height of 575 mm (IRC – SP: 72 – 2007).

Dynamic cone penetrometer test
Dynamic cone penetrometer test

The amount of cone penetration (in mm) is usually reported as DCIP in terms of average penetration per blow. It indicates the relative shear strength of the material at the depth tested. During cone penetration, the material’s shear strength is accrued primarily due to the resistance offered by the shear displacement of soil particles.

Factors Affecting DCPT Result

1. Alignment of DCP Rods

When testing, the rods below and above the DCP should be straight and the cone should be seated freely in the position of the test material. If the penetrating rod is inclined during rest, the resistance (i.e. skin friction) around the rod will increase due to contact with the confined pavement layers which causes a decrease in the rate of penetration. Such a situation can also occur when the DCP rod penetrates through the collapsible granular material.

2. depth of test

DCP test results are very sensitive to the depth of the test. When the lower rod of the DCP used is longer than the standard penetrating rod, an improvement in the DCPI value should be applied because the vertical confinement and skin friction around the rod increase the resistance of the penetrating rod. When the granular layer is tested with DCP, the effect of vertical confinement due to the asphalt layer has been found to be significant.

3. damaged cone tip

If the cone tip of the DCP is damaged it will give wrong test result.

4. top angle of cone

30. The penetration rate will be significantly affected by the change of cone apex angle from0 from 600 Since a conical surface with an upward frictional force of 600 The top angle will be bigger. From experiments it is found that the cone apex angle by DCP is 30. penetration rate achieved with0 60. 10% more than that obtained with a cone having vertex angle of0,

5. hammer weight

The hammer should weigh exactly 8 kg. If the hammer weight is less than specified, the rate of penetration will decrease and vice versa.

6. Hammer Lifting Height

During the DCP test, for each strike, the hammer weight must be raised to the top restraint plate and dropped freely. During the test, if the hammer is not raised to a given standard height, the impulse force exerted by the cone will decrease and the penetration values, in turn, will decrease.

7. moisture content

DCP test results are very sensitive to variations in the amount of moisture present in the test material. As the moisture content increases, the penetration rate of DCP also increases and vice versa. For this reason, DCP tests are carried out during the post-monsoon seasons when the granular and sub-grain layers become soft and their minimum strength is recorded.

8. material composition

The DCPI test varies with material composition, class of soil, coefficient of curvature, uniformity, density of layer material and plasticity of soil.

9. intensity of compaction

DCPI will be affected by the intensity of compaction and delamination of the granular and sub-grade layers.

Er. Mukesh Kumar

Photo of author
Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.