This contribution investigates the characteristics of elastic wave velocities (Vp and Vs) during triaxial shearing tests under dry and drained conditions. Samples of tested materials with different particle morphologies (i.e., particle shape and surface roughness) were prepared under three strategies, namely, similar initial void ratios (e0), relative densities (Dr0), and side tapping numbers (Nt). Regarding the elastic wave velocities as functions of e0 and confinement r at very small strain ranges, i.e., V = a(B - e0)(r 1kPa)b, a was seen to increase for more angular materials or smoother surfaces, while b and B were seen to decrease as the particles became more angular or the surfaces became smoother. During triaxial shearing, Vp increased initially and then tended to decrease more gently, whereas Vs increased initially and then showed a marked decrease before convergence upon shearing regardless of the e0 for the given material. The influence of particle morphology on the absolute values for Vp and Vs was found to be complex during shearing, whereas the wave ratio (Vp/Vs) was consistently greater under rougher conditions for the same shape. Importantly, the wave ratio (Vp/Vs) was found to correlate well with the particle morphology: more angular materials and rougher surfaces exhibited a greater Vp/Vs ratio normalized by the stress and density conditions for each material, which further indicates a higher degree of fabric anisotropy with reference to the microscopic evidence in the literature. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BYNC -ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

One of NASA priorities is the in-situ exploration of ocean worlds in the solar system where potentially there might be life under the ice shell. This requires reaching the ocean below extremely cold through significant deep ice. Jupiter's moon, Europa, is such a challenging body, where it is estimated to have a 40 km thick ice shell. An approach for reaching the ocean has been conceived using a melting probe Cryobot concept that has been studied for a potential future mission. A lander is assumed to be the platform from which the Cryobot would be deployed. The ice penetrating vehicle concept consists of a cylindrical, narrow-body probe that encases a radioisotope heat/power source that would be used to do the penetration by melting through the icy crust. The baseline design of the probe includes a suite of science instruments to analyze the ice during descent and the liquid ocean underneath. For communication, a set of fiber optic wire as well as wireless RF in the very cold porous top layer is assumed, and then acoustic modules would be used for the communication in warmer denser ice over distance of 25 km between the modules. In addition to the acoustic communication modules, a sonar is part of the concept, for obstacle avoidance. The focus of this paper is on the use of elastic waves in the 1kHz range.