ISO 17892-6:2017 specifies a method of undrained strength index testing of both undisturbed and remoulded specimens of fine grained soils by the fall cone method.

ISO 17892-6:2017 is applicable to the laboratory estimation of undrained shear strength of a soil test specimen within the scope of geotechnical investigations.

In the fall cone test, a cone is allowed to fall with its tip towards a soil specimen, and the resulting penetration of the cone into the soil is measured. The penetration values are used to estimate the undrained shear strength. The fall cone test produces a complex shear in the test specimen, and does not represent either a vertical triaxial compression or a horizontal shear test. However, this index test may be correlated to some estimate of undrained shear strength determined in the laboratory by other test methods.

As the test is performed on a small laboratory specimen, the result may not agree with laboratory tests on larger specimens. In addition, the test specimen may not be fully representative of the soil in its natural state in the field; for example, the test specimen may not have fissures present in situ at a larger spacing than the specimen size.

Therefore, for the above reasons, the test can be regarded as an estimation of undrained shear strength, rather than a true measurement of it.

The ratio of the remoulded shear strength to the undisturbed shear strength may be used to estimate the sensitivity of a soil specimen. Time-dependent measurement of the shear strength may be used to assess the thixotropic regain of strength of a remoulded soil specimen.

NOTE This document fulfils the requirements of the strength index testing of soils for geotechnical investigation and testing in accordance with EN 1997?1 and EN 1997?2.