5:15 PM - 6:30 PM
[SSS02-P13] Strength and mechanical behavior of the Nankai accretionary prism sediments from NanTroSEIZE Expedition 348
Keywords:Accretionary prism, Indentation test, IODP, Expedition 348
We adapted this method to investigate the depth profile of mechanical property along Holes C0002N and C0002P, the Nankai accretionary prism. We conducted spherical indentation experiments on the hand-picked intact cuttings retrieved from 870 to 3058 meters below seafloor (mbsf) at Site C0002. We used a spherical sapphire indenter with a diameter of 4 mm to deform the cuttings sample of >2mm thickness saturated with brine at room temperature and pressure conditions with a constant loading/unloading rate of 0.5 N/sec and maximum load of 100 N. Using the correlations mentioned above and assuming internal friction value that may be correlated with porosity, we estimated in-situ Young’s modulus and strength of the sediments at Site C0002. The Young’s modulus increases from ~0.5 GPa at 870 mbsf to ~2.2 GPa at 2000 mbsf, then it becomes nearly constant at ~2.2 GPa below 2000 mbsf. The failure strength under in-situ pressure condition increases with depth from a few MPa at 870 mbsf to ~70 MPa at 3000 mbsf. The results of the failure strength are consistent with that obtained by triaxial compression tests on discrete core samples collected from ~2200 mbsf under in-situ pressure and temperature conditions. The result indicates the possibility that strength of sediments which is commonly determined by triaxial experiment can be reasonably estimated from drill cuttings using a spherical indentation test.