Tuaheni submarine landslide complex geotechnical laboratory testing of cores from holes Tan14014-02 and Tan1404-10 factual report

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Lyndsell, B.M.; Barker, P.R. 2016 Tuaheni submarine landslide complex geotechnical laboratory testing of cores from holes Tan14014-02 and Tan1404-10 factual report. Lower Hutt, N.Z.: GNS Science. GNS Science report 2016/04; RS lab report 004 iii, 14 p.

Abstract: Active landslides are a known geohazard in submarine environments, although the mechanism that causes submarine landslides to fail remains poorly constrained. This factual report aims to provide new knowledge of physical and geotechnical properties and present one of the first conventional geotechnical datasets for the Tuaheni Landslide Complex located on the Hikurangi Margin, off the east coast of the North Island, New Zealand. This report outlines a suite of geotechnical laboratory tests conducted on off shore gravity cores obtained from two sites within the Tuaheni Landslide Complex that were provided by NIWA for testing at the GNS Science Rock and Soil Mechanics Laboratory, Lower Hutt. The testing suite is comprised of physical properties testing (water content, void ratio, dry density, bulk density and Atterberg Limits) and shear strength testing (using a direct shearbox and hand shear vane) to better understand these landslide materials. The results of the geotechnical testing are presented in a series of tables and graphs. These outputs show the samples have high plasticity (Plasticity Index >40) and lie on the boundary between silt and clay. The shallow sampling depths (2 m) are reflected by the average dry density values of 0.6 and 0.9 t/m3, as well as the void ratios of 3.1 and 2.1, respectively. The shear vane strengths of the samples are ≤7 kPa which may classify the soil as very soft and reflect the high ‘as received’ water contents. Shearing in the direct shearbox was performed on single specimens at three different normal loads of 10, 32 and 76 kPa. No peak strength was observed throughout a minimum of five shear reversals. The shear strength envelopes indicate a cohesion value of 4 kPa and friction angles of 34° and 36°. (auth)