How strong was Goliath? Geomechanical characterization of the submarine Goliath slide

Understanding the mechanical properties of continental submarine slopes is critical for the assessment of geo-marine slope stability hazards. This paper presents the first detailed geomechanical study on sediment profiles associated with a geologically recent sliding event at the Goliath submarine complex offshore southern Israel. Sediment samples were extracted from ~ 5-m-long piston cores collected from three representative sites: on the recent slide headscar (PHS3), the adjacent undisturbed slope seafloor (PSL4), and at the dextral tail-depositional lobe (PTL3). The investigation included Gamma-ray and CT scanning, sediment phase measurement, laboratory T-bar penetration, and vane shear testing. The evaluated properties for the three sites are the undrained shear strength, over-consolidation ratio, soil sensitivity, water content, and density. The experimental results show a strong correlation between the findings of the various investigation tools regarding the original soil condition before sliding, the slide scar location, the degradation in properties of the disturbed soil, and the post-slide deposited soil properties. Despite the variation in properties among the different sites, the paper presents a prediction model for the soil strength in the Goliath slide area. Beyond the geomechanical characterization, the analysis of the test results highlights two unique findings: (1) evidence of a long-term strength softening phenomenon in the post-slide period, and (2) insights into the transition of geomechanical properties with depth within the slide scar.