Nondestructive Testing of Stabilized Soils and Soft Rocks via Needle Penetration

Assessing the strength of hard soils and soft rocks is a pressing issue in geotechnical investigations, since high quality core samples recommended by testing standards for strength determinations cannot always be achieved. As a solution, a light-weight, non-destructive testing device, Needle Penetrometer (NP), was developed in Japan. It is not well known and standardized in other parts of the world. No sample preparation is required, and it is applicable both in the field and laboratory with minimum surface conditioning. This study aims to provide some new contributions to previous works on the NP test, including new rock types and stabilized soils. For these purposes, unconfined strength (UCS) and needle penetration resistance (NPR) values were determined for compacted clays, lime and cement stabilized clays, micritic tufa, microdetrital tufa and pumice. A database consisting of a total of 108 UCS–NPR data pairs was established. Regression analyses reveal that, there is a significant relationship between UCS and NPR. It is concluded that the NP tests can be applied to stabilized soils and soft rocks with UCS of up to 30 MPa to predict the UCS from NPR.