Static Cone Penetration Test
Principle
This test involves forcing a cone into the ground and measuring the pressure needed for each
increment of penetration. The result is expressed in the form of cone resistance (qc) in kgf/cm2.
Since the cone is pushed rather than driven, the test is also known as static cone penetration test
(SCPT).
Dutch cone test: The most commonly used cone test is the Dutch cone test. The Dutch cone has an
apex angle of 60° and a base area of 10 cm2.
Test Procedure
For obtaining the cone resistance, the cone is pushed downward at a steady rate of 1.5–2 cm/s. The
resistance offered by the soil to the penetration of the cone is directly measured in kgf/cm2 and
recorded as cone resistance (qc).
Types of Penetrometers
The following two types of cone penetrometers are available for cone testing:
1. Mechanical penetrometer.
2. Electrical penetrometer.
The electrical penetrometer gives a continuous record of the penetration resistance and hence
reflects better the nature of the soil layers penetrated. The repeatability of the cone test is also good
with the electrical penetrometer. But, it requires skilled operators and better maintenance and also
it is costlier than mechanical penetrometers.
Correlation with Engineering Properties
Table shows the correlation of qc with SPT N, which helps in correlation with other Engineering
properties. IS:6403–1981 recommends a method for determination of ultimate bearing capacity of
soil using static cone penetration resistance (qc) for cohesionless soils as well as cohesive soils.
Table Relation between qc and N
Type of Soil qc/N
Sand and gravel mixture 6
Sand 4
Sandy silts 3
Clay–silt–sand mixtures 2
Insensitive clays 1.5
Advantages
Some of the advantages of the cone penetration testing are the following:
1. It is very rapid; the speed of operation allows considerable data to be obtained in a short
period of time.
2. The use of electrical penetrometers allows precise measurements.
3. It is very useful in very soft soils, where recovery of undisturbed samples would be very
difficult.
Disadvantages
Some of the major drawbacks of CPT are as follows:
1. It is not possible to recover samples for identification.
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2. It is difficult to advance cone in dense or hard deposits.
3. A stable and fairly strong working surface to support the rig is needed for conducting the
cone test.
4. The method is applicable only in fine-grained deposits (clay, silt, and fine sands), where the
material does not have massive resistance to cone penetration.
Suitability
SCPT is most successful in soft or loose soils, such as silty sands, loose sands, and layered deposits of
sands, silts, and clays, as well as in clayey deposits.
Dynamic Cone Penetration Test
In this test, the cone is driven into the ground by application of blows with a 65-kgf hammer, falling
through a height of 75 cm, instead of pushing. Cone resistance (Ncd) is measured in terms of the
number of blows per 30-cm penetration.
Dynamic cone penetration test (DCPT) is of the following two types:
1. Dry DCPT.
2. Wet DCPT.
Dry DCPT is performed using a 5-cm-diameter cone without bentonite slurry [IS:4968 (Part I)]. Wet
DCPT is performed using a 6.5-cm-diameter cone with bentonite slurry [IS:4968 (Part II)].
