What is the weight and drop height of the hammer used in this test?

The standard specifies a 65 kg hammer with a free fall of 75 cm (Clause 3.1).

What does the Nc value from a DCPT represent?

Nc is the number of blows required to drive the cone through a depth of 10 cm (Clause 4.1).

What are the dimensions of the cone?

The cone has an apex angle of 60 degrees and a base diameter of 50 mm (Clause 3.1.5).

Is this test suitable for all soil types?

No, it is not recommended for gravelly soils or ground containing boulders, as this can damage the cone and produce misleadingly high resistance values (Note under Clause 4.1).

IS 4968 Part 2

: 1976

Method for subsurface sounding for soils - Dynamic cone penetration test

CurrentFrequently UsedTesting MethodBIMGeotechnical · Soil and Foundation

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This standard specifies the method for conducting the Dynamic Cone Penetration Test (DCPT) for subsurface soil exploration. It details the apparatus, including the 65 kg hammer with a 75 cm drop and a 60-degree cone, the test procedure, and the method of recording and presenting results. The test measures the number of blows (Nc) required to drive the cone a specific distance, providing an indication of soil resistance.

Describes the method for conducting the dynamic cone penetration test (DPT) for subsurface investigations.

Quick Reference Values

Weight of driving hammer65 kg

Free fall height of hammer75 cm

Cone apex angle60 degrees

Cone base diameter50 mm

Penetration increment for recording blows10 cm

Practical Notes

This is the 'Heavy' DCPT, distinct from the lighter versions used for pavement subgrade analysis. The 65 kg hammer is the key differentiator.

The test is faster and more mobile than the Standard Penetration Test (SPT), making it suitable for preliminary investigations or sites with difficult access.

Results (Nc values) are often correlated with SPT 'N' values and soil parameters like CBR, but these correlations are site-specific and should be used with caution.