Free fall penetrometer tests in sand: Determining the equivalent static resistance

Abstract

Free Fall Penetrometer (FFP) tests provide an efficient way to determine the penetration resistance at shallow depths in sandy soils, and are being used increasingly in geotechnical,geomorphological and coastal engineering applications. A limitation of free fall penetrometers is the effect of their high velocity on the penetration resistance. This affects the drainage condition, creates aviscous-type enhancement of the mobilised strength, and also introduces inertial drag forces. It is useful ifthe measured FFP resistance can be adjusted back to the resistance that would be expected in a standard Cone Penetrometer Test (CPT) at the same location. With this adjustment, the resistance can be used in the same correlations and design methods as standard CPT data. Adjustments for viscous-type rate effects and inertial drag have been proposed and explored in detail for clay soils. The contribution of this paper is to outline a correction scheme for drainage condition, which is more relevant for sandy soils.This correction utilizes the dissipation response at the end of the FFP test, in combination with the measured or derived FFP tip resistance. Relationships for penetration resistance in drained and undrained conditions based on density state are developed. It is shown that the high velocity FFP resistance can be uniquely mapped to a resistance from a standard CPT, when combined with the dissipation response. With development and validation, this new framework could enhance the value of FFPs as a complementary or alternative technology alongside conventional static penetration testing

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ORCID for D.J. White: orcid.org/0000-0002-2968-582X

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