Numerical Modelling of Free Fall Penetration of a Spherical Penetrometer in Sand

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4. Numerical Modelling of Free Fall Penetration of a Spherical Penetrometer in Sand

In the recent past, Free Fall Penetrometers (FFPs) have emerged as useful offshore site exploration tools for characterizing shallow depth sediments. FFPs are simple to design and easy to deploy. Studies have reported the use of different shapes of FFPs for characterizing both sandy and clayey soils. While the use of conical FFP with a shaft is more common in the existing literature, researchers have also reported the use of shaftless spherical FFPs. FFPs deployed in the field are generally fitted with inertial measurement units including accelerometers and gyroscopes. The measured deceleration time history can be related to the mechanical properties and state of the soil. In this paper, Coupled Eulerian Lagrangian formulation of the commercial package Abaqus has been used to simulate the penetration of a spherical FFP in dry sand. The impact of the free-falling sphere is simulated by assigning an initial velocity. A Modified Mohr-Coulomb model is used to capture the dilative response of sand based on its relative density. A parametric study is carried out for a range of relative density, critical state friction angle of the sand and impact velocity of the FFP. It was observed that the peak deceleration increases with increasing relative density, critical state friction angle, impact velocity and the mass of the penetrometer. The observed trend has been presented in simple charts and can be useful in interpretation of frictional property and state of near-surface sandy deposits.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

2 - Site characterization, in-situ and laboratory testing, measurement