Evaluation of Mechanical and Physical Characteristics of Aquatic Muds by Geotechnical Methods, for Assessment of Methane Bubble Descriptor

The physical and mechanical characteristics of gas-free aquatic muds govern methane bubble descriptors such as size, shape, and orientation. Here, we quantify these mud characteristics in Lake Kinneret (Israel) using four gravity cores (A, B, C, and D: 1.5 to 2.45 m length, taken along few hundred meters at NW transect from 27.5 to 38 m water depth). Depth-dependent undrained shear strength was measured using a pocket shear vane and was also estimated numerically, both showing an increasing trend with depth, with maximum values of 1.8 kPa (A at 1.55 m), 1.6 kPa (B at 1.75 m), 4.7 kPa (C at 2.33 m), and 2.7 kPa (D at 2.15 m). The suspension–sediment interface corresponded to density transitions at ρ = 1.28 g/cm³ at 0.675 m (A), ρ = 1.27 g/cm³ at 0.775 m (B), ρ = 1.20 g/cm³ at 0.625 m (C), and ρ = 1.11 g/cm³ at 0.525 m (D). Basic geotechnical index properties indicate water-rich, highly porous muds: water contents decrease with depth (including within suspension zone) from 329% to 122% (A), 311–109% (B), 372–112% (C), and 461–116% (D); porosity falls from ~90 near the top of the cores to ~76% at 1.75 m (A) and 1.55 m (B), and from >85–90% at the tops of cores C and D to ~70–75% at their bases. Atterberg limits are nearly constant, with LL ≈ 67% and PL ≈ 37% in cores A and B, and LL ≈ 75%, PL ≈ 32%, and an average PI ≈ 43 in cores C and D, consistent with high-plasticity silty clays. Dynamic Young’s modulus, evaluated from ultrasonic P-wave velocities, yielded irregular profiles in intact cores (ranging between ~500 m/s and ~1490m/s), which we attribute to presence of cracks and voids (from which methane gas escaped at the core retrieval), whereas remolded muds where the voids were eliminated, exhibited a monotonic increase in sound speed with depth, in the range from 1462m/s to 1492m/s. Further, Young’s modulus, small-strain shear modulus, and Mode I fracture toughness were derived from the Atterberg limits, while fracture toughness was inferred from empirical correlations with shear strength. Overall, our results demonstrate that Atterberg limits and basic geotechnical indices provide an effective framework for predicting small-strain stiffness and fracture properties of the aquatic muds, offering essential input for improved quantification of methane bubble descriptors in acoustic models.