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We conducted constant rate of strain (CRS) consolidation tests on 16 whole-round samples obtained during Integrated Ocean Drilling Program (IODP) Expeditions 315 and 316 as part of Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Stage 1 drilling. Samples were taken from slope sediments and the underlying accretionary wedge cored at IODP Sites C0001, C0004, and C0008 in the vicinity of a major out-of-sequence thrust fault (termed the megasplay). We conducted tests in parallel at the Rock and Sediment Mechanics Laboratory at The Pennsylvania State University (USA) and the geotechnical laboratory at the University of Missouri (USA), with the objectives of (1) defining the compression behavior and hydraulic properties of the sediments and (2) estimating in situ effective stress and pore pressure conditions from laboratory stress-strain behavior. In addition, we conducted quantitative fabric analyses at the University of Missouri on samples taken immediately adjacent to the CRS test specimens using an environmental scanning electron microscope. The samples exhibit similar consolidation and hydraulic properties. The samples exhibit a general trend of increasing fabric development with depth at Sites C0004 and C0008, with samples from the accretionary prism at Site C0001 and slope sediments in the footwall of the megasplay fault at Site C0004 exhibiting a higher degree of grain alignment. The compression index ranges from 0.419 to 1.058 for the entire suite of samples, with most values ranging from 0.6 to 0.8. Intrinsic permeability decreases systematically with increasing effective axial stress and decreasing porosity and varies log-linearly with porosity. The permeability-porosity trends for specimens from the three sites are similar and exhibit no systematic variation with depth. Estimated values of in situ hydraulic conductivity follow a similar trend at all three sites and decrease with depth from values of 3.3 × 10–10 to 1.0 × 10–9 m/s at ~50 meters below seafloor (mbsf) to 3.3 × 10–11 m/s at 440 mbsf. We estimated maximum preconsolidation stress (Pc′) using two separate techniques and consistently obtained values comparable to calculated values of hydrostatic vertical effective stress at Sites C0001 and C0008. Similarity of these values is consistent with normal consolidation and hydrostatic pore fluid pressures. In contrast, Pc′ values for Site C0004 document apparent overconsolidation. doi:10.2204/iodp.proc.314315316.218.2011 D. Saffer et al. Data report: consolidation, permeability, and fabric of sediments Introduction The Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Experiment (NanTroSEIZE) project is a multiexpedition, multiyear complex drilling project aimed at understanding the mechanics of subduction zone faulting and earthquakes through a combination of coring, logging, downhole measurements, and observatory installation, coupled with allied geophysical surveys and laboratory experimental studies (Tobin et al., 2009). As part of operations during NanTroSEIZE Stage 1, core samples were collected at several riserless drill sites for postexpedition laboratory study (Ashi et al., 2009; Screaton et al., 2009a). The compression behavior and hydrologic properties of marine sediments are particularly relevant to the objectives of the NanTroSEIZE project because they exert fundamental control on subseafloor fluid flow, consolidation and dewatering, and the potential generation of excess pore pressures in response to loading by rapid sedimentation and/or tectonic compression. Here, we report on laboratory consolidation testing of samples collected at IODP Sites C0001, C0004, and C0008 in the vicinity of the “megasplay” fault, a major out-of-sequence thrust (OOST). The fault cuts the accretionary wedge and extends >120 km along strike, and it has been implicated in coseismic slip (Fig. F1) (e.g., Park et al., 2002; Moore et al., 2007). Thus, the megasplay fault is a primary drilling target for the NanTroSEIZE program. Site C0001 sampled the hanging wall of the megasplay fault, and Site C0004 penetrated through the fault into the footwall, which consists of underthrust slope-apron deposits (Expedition 314 Scientists, 2009a, 2009b; Expedition 315 Scientists, 2009b; Expedition 316 Scientists, 2009a). Site C0008 sampled mildly disturbed slope-basin sediments resting above accreted trench-wedge deposits (Expedition 316 Scientists, 2009b). Figure F2 shows the stratigraphic and structural context of all sampling intervals, as well as the dip of bedding in close proximity to the samples. We obtained 16 whole-round core samples from the drill sites and conducted constant rate of strain (CRS) consolidation tests in order to define (1) sediment compression behavior, (2) the maximum in situ effective normal stress (Pc′), and (3) sediment permeability and hydraulic conductivity. Here we report the results of 19 CRS tests, conducted on 16 wholeround core samples (and including three repeat experiments to assess experimental reproducibility) (Table T1). In addition, we conducted quantitative fabric analyses at the University of Missouri (USA) on samples taken immediately adjacent to the CRS test specimens using an environmental scanning electron microscope (ESEM) to image grain fabrics Proc. IODP | Volume 314/315/316 within horizontally and vertically oriented surfaces. Evaluation of microfabric images needs to take bedding dips into account, as shown in Figure F2. We combine results from tests conducted following the same experimental protocols at two institutions: the Rock and Sediment Mechanics Laboratory at The Pennsylvania State University (USA; herein referred to as PSU) and the geotechnical laboratory at the University of Missouri (MU). All notations for this report are summarized in Table T2; sample information and a summary of experimental results are shown in Table T3. Results from fabric analyses are shown in Table T1. Experimental data for each CRS test are provided in CRS in “Supplementary material.” Experimental methods Sample handling and preparation During the drilling expeditions, whole-round samples of ~10–20 cm length were selected for postexpedition geotechnical tests using X-ray computed tomography (CT) scans to identify minimally disturbed intervals of hemipelagic mud/mudstone. Whole-round samples were sealed in plastic core liners using plastic caps and electrical tape, sealed within aluminum vacuum bags with wet sponges to minimize desiccation, and stored in a refrigerator until the end of the expedition. At that time, samples were shipped with cold packs by courier to the PSU and MU laboratories, where they were kept refrigerated until they were trimmed and used for CRS tests. After removing whole-round samples from the core liner, we carefully trimmed cylindrical specimens to fit in the fixed steel ring of an oedometer system (Fig. F3) using a sharp stainless steel cutting shoe (to cut the specimen to the exact ring diameter) and a wire saw and trimming jig to attain flat top and bottom specimen faces. The specimen diameter for PSU tests was either 50 mm or 36.6 mm, depending on the test, and the specimen diameter for MU tests was 41 mm (Table T3). The initial specimen height was ~20 mm for PSU tests in most cases and ~24 mm for MU tests. During specimen preparation, we took trimmings for measurement of water content and initial void ratio (ASTM International, 2006; Long et al., 2008). We determined specimen water content and void ratio from wet mass and dry mass after oven drying at 105°C for 24 h, following the IODP method used for moisture and density (MAD) measurements that accounts for salt mass in seawater (Blum, 1997; Expedition 315 Scientists, 2009a). These values are reported in Table T3. In addition, we obtained a second measurement of index proper2 D. Saffer et al. Data report: consolidation, permeability, and fabric of sediments ties after completion of the CRS test by oven drying the test specimen in the steel ring and using the same method. After trimming, we placed specimens in the fixed ring of the oedometer system and deaired the system and pore fluid lines using a vacuum pump. We then backpressured the specimens to values of ub = ~200 kPa (MU) or ub = ~300–400 kPa (PSU) using deaired synthetic seawater for 24 h to ensure saturation and to dissolve any air remaining in the lines. To maintain contact between the loading ram and specimen and to prevent swelling during backpressuring, we held the axial load at a value ~10–20 kPa higher than the backpressure to maintain an effective axial stress (σa′) of <25 kPa for the PSU tests and specified the axial stress to maintain a condition of 0.2% axial strain for the MU tests. Consolidation test procedure and computations We conducted CRS tests at the two laboratories, following the protocols and test configuration specified by the American Society for Testing and Materials (ASTM) (ASTM International, 2006). In our CRS tests, we deformed the specimen at a constant rate of strain, controlled via a specified displacement rate boundary condition applied by a computer-controlled load frame (Fig. F3). The sample is confined in a steel ring to maintain a condition of zero lateral deformation (i.e., uniaxial strain), is undrained at its base, and is open to backpressure (ub) at its top. During each experiment, we continuously monitored specimen height (h), total axial stress (σa), and basal pore pressure (u). Tests were run to peak axial stresses of ~20 MPa at MU and either ~20 or ~40 MPa at PSU. For each test, we chose the displacement rate (or strain rate) to maintain an anticipated ratio of basal excess pore pressure to a total axial stress (Δu/σa) less than ~0.10. Strain rates for the tests are shown in Table T3. We recorded the loading phase for all tests and the unloading phase for a subset of the experiments; these results are shown in the stress-strain and stress-void ratio curves in Figures F4, F5, F6, F7, F8,

Data report: consolidation, permeability, and fabric of sediments from the Nankai continental slope, IODP Sites C0001, C0008, and C0004