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doi:10.2204/iodp.proc.314315316.213.2011

Introduction

Consolidation characteristics of marine sediments and sedimentary rock are used to evaluate diagenetic, hydrologic, and compaction processes during subduction and accretion (e.g., Lee et al., 1973; Trabant et al., 1975; Carson, 1977; Shepard and Bryant, 1977; Taylor and Bryant, 1985; Morgan and Ask, 2004; Spinelli et al., 2007). Greater-than-expected states of consolidation can result from tectonically induced (nonvertical) stress, deformation, cementation, and/or uplift and erosion of overburden, whereas underconsolidation (values less than expected) can be caused by excess pore water pressure (i.e., greater than hydrostatic) and the presence of gas and gas hydrates. Consolidation tests also provide estimates of in situ fluid pressure, permeability, and bulk sediment compressibility (Karig, 1996; Saffer et al., 2000; Stump and Flemings, 2002).

As part of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), we conducted 18 constant-rate-of-strain consolidation (CRSC) tests on 17 whole-round (WR) core samples from Integrated Ocean Drilling Program Sites C0002, C0006, and C0007. The sites are located along the Kumano transect offshore south-central Japan (Fig. F1), and they were drilled during Expeditions 315 and 316 (see the “Expedition 315 Site C0002” [Expedition 315 Scientists, 2009], “Expedition 316 Site C0006” [Expedition 316 Scientists, 2009b], and “Expedition 316 Site C0007” [Expedition 316 Scientists, 2009c] chapters). The CRSC tests were conducted to obtain the one-dimensional compression characteristics of the sediments, values of hydraulic conductivity and permeability, and an assessment of the consolidation state (maximum vertical effective stress). We followed essentially the same testing protocols at two institutions: Geotechnical Laboratory at the University of Missouri (MU; USA) and the Rock and Sediment Mechanics Laboratory at The Pennsylvania State University (PSU; USA).

The microfabric of sediments and sedimentary rocks can influence their physical properties and compressibility (Avseth et al., 2000; Sunderland and Morgan, 2003). It is also noteworthy that natural clay-rich sediments and lithified shales show large ranges in permeability values, and this can be attributed to their differences in mineral composition, texture, and grain fabric (Bennett et al., 1991; Neuzil, 1994; Dewhurst et al., 1999; Yang and Aplin, 2007). To gather such information for the NanTroSEIZE samples, we used an environmental scanning electronic microscope (ESEM) to quantify the alignment of grains on faces cut parallel to (vertical) and perpendicular to (horizontal) the core axis.

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