Abstract: As a new type of geological investigation technology, free-falling penetrometer (FFP) can obtain the mechanical properties of seabed sediments efficiently and quickly. During the FFP penetration process, the measured cone tip resistance is significantly influenced by the penetration rate. To process the data, it is essential to convert the dynamic penetration resistance into a quasi-static penetration resistance equivalent to the static penetration resistance of the cone penetration test (CPT). A rate factor correction related to the penetration rate is crucial for data analysis. This paper conducts theoretical analysis of rate effect based on Newton's Law of Motion, and examines mucky soil on the northern slope of the South China Sea through laboratory testing. Logarithmic function and power function are employed to fit the relationship between cone tip resistance and penetration rate, a calibration method for the correlation coefficient of free-falling penetration instrument rate is proposed. Findings indicate that both the release height and the probe quality affect the final penetration depth, but the change of cone tip resistance during penetration is less affected by the probe quality. The method proposed in this paper accurately determines the rate correlation coefficient of FFP penetration. The coefficient, calibrated through laboratory tests, can rectify in-situ test data in practical scenarios, offering technical support for FFP applications.

Key words: seafloor sediments, free-falling penetrometer, sediment strength, marine geological survey