Free-fall penetrometers (FFP) are time-efficient and cost-effective tools for estimation of seabed strength parameters. However, the accuracy of strength parameters are coupled affected by the strain-rate effect, the strain-softening effect and the hydrodynamic drag on the FFP. A modified free-fall ball penetrometer with a booster (FFBPB) was put forward in the present study for the convenience of measuring the strength of soils with deep embedment depth. Numerical analyses based on the computational fluid dynamics (CFD) approach were conducted in the present study to investigate the complex ball-soil interaction, from which the expressions of the strain-rate factor, drag coefficient, and added mass were established. Then a back-analyses framework was developed to estimate the strength parameters, including the original undrained shear strength, strain-rate parameter, and strain-softening parameters, based on the measurements from the FFBPB. Finally, a series of model tests were performed to validate the back-analyses framework. The back-analysed strength parameters are considerably consistent with that from quasi-static tests, indicating the reliability of the back-analyses framework.

自由落体渗透仪（FFP）是用于估算海底强度参数的省时，划算的工具。但是，强度参数的准确性受应变率效应，应变软化效应和对FFP的流体动力阻力的影响。为了方便测量深埋深的土壤强度，本研究提出了一种带有助推器的改进型自由下落球渗透仪（FFBPB）。本研究基于计算流体动力学（CFD）方法进行了数值分析，以研究复杂的球-土相互作用，从而建立了应变率因子，阻力系数和附加质量的表达式。然后，建立了一个反向分析框架来估算强度参数，包括原始的不排水剪切强度，应变率参数和应变软化参数，基于FFBPB的测量结果。最后，进行了一系列模型测试以验证反向分析框架。反向分析的强度参数与准静态测试的参数相当一致，表明了反向分析框架的可靠性。