Parallel Session C-4: Offshore geotechnics - Chair: Hadrien Rattez

Permeability (or hydraulic conductivity) is one of the most important parameter for analyzing hydraulic behavior of underground.This study summarizes the methods and parameters used to estimate permeability using Nuclear Magnetic Resonance signals from hydrate-bearing sediment obtained from logging and laboratory tests for the Gulf of Mexico and Alaska North Slope. In addition, we reports parameters for predicting model for muddy sediments which was recovered from overburden of hydrate-reservoir in the Hyuganada sea in 2022 Japan.

Accelerating advancements in robotic engineering provide an opportunity for developing economical and efficient site characterisation devices, particularly for offshore applications. A new intelligent robotic device, ROBOCONE , is being developed for site characterisation and design of offshore structures considering “whole life” stress strain histories. ROBOCONE could apply lateral, shear, and torsional modes of loading on the surrounding soil. The lateral module behaviour of the ROBOCONE device under various stresses, without boundary effects, is studied in the light of 3D Discrete Element Modelling (DEM), developing an understanding of the physical capacity of the robotic device in sustaining the lateral forces.

A new miniature T bar penetrometer is designed and fabricated for physical modelling, allowing the characterization of the undrained shear strength profile of clay samples in centrifuge testing. The rate of penetration is one of the key parameters that govern the drainage behaviour of soil response around the T bar and the resulting penetration resistance. Thus, the sample drainage state is tested by varying the rate of penetration from 0.004 mm/s to 5 mm/s. The results are interpreted by two methods. The interpreted undrained shear strength profile provides soil property and OCR information for further monopile tests in the centrifuge.