Data report: preliminary assessment of Pleistocene sediment strength in the Ursa Basin (Gulf of Mexico continental slope) from triaxial and ring shear test data

Abstract

We report the preliminary results of a triaxial and ring shear study on clay-rich, fine-grained Pleistocene sediments cored in Ursa Basin, Gulf of Mexico continental slope. Specimens from Integrated Ocean Drilling Program (IODP) Expedition 308 Sites U1322 and U1324 document friction coefficients in the range of 0.13-0.31, with internal angles of friction of ~7.4°-17.2° in ring shear experiments. At intermediate (7.624 MPa) to high (15.237 MPa) overburden pressure, the majority of the samples tested show velocity weakening, whereas lower overburden pressures do not give a clear trend regarding velocity weakening or strengthening of the samples. In consolidated-undrained triaxial tests, peak shear stresses observed are between 27 and 140 kPa, with the strongest sample by far coming from a core catcher section. We suspect that this is an effect of fabric changes induced during hydraulic piston coring. One sample coming from the base of a mass transport deposit at Site U1322 is the weakest one tested. Young's moduli calculated range from 2 to 17.4 kPa. Stress paths indicate slight overconsolidation of the samples, which is in line with the information gained from preconsolidation stresses in other studies. Permeability determined from consolidation data is in the range of 10

Crack extension induced by dissociation of fracture-hosted methane gas hydrate

“…We use a modulus of E = 150 kPa in the computation which is consistent with the measurement of Johnson et al []. Other experimental studies showed that Young's modulus varies from midteen kilopascal [ Meissl et al , ] to hundreds of kilopascals [ Barry et al , ]. As noted earlier, the crack opening for other values of Young's modulus can be obtained from the numerical results for E = 150 kPa.…”

Petrophysical and consolidation behavior of mass transport deposits from the northern Gulf of Mexico, IODP Expedition 308

“…Triaxial experiments on sediments from Sites U1322 and U1324 also show contractional behavior during shear, which would lead to densification. Triaxial experiments by Meissl et al (2010) document contraction during shear for relatively small axial strains (~2%) followed by dilation at higher axial strains; this dilational response, however, was likely controlled by the experiments being conducted on samples in an overconsolidated state. Triaxial compression tests on normally consolidated samples (overconsolidation ratio = 1) showed contraction during shear for axial strains up to 20% ).…”

Submarine Mass Movements and Their Consequences

“…Four samples come from Site U1324, and represent normally sedimented material from a variety of settings (Flemings et al 2006). Meissl et al (2010) infer that additional consolidation may have been applied to the sample by the piston coring process. Peak shear stresses are very small , and corroborate the shipboard results (see logs in Fig.…”

“…Measurements were performed with axial loads ranging from approximately 2 MPa to approximately 16 MPa at four rates of shear, starting with 0.014 or 0.005 mm/min, then accelerating to 0.18 mm/min, then to 1.8 mm/min, and finally slowing down to 0.005 mm/min (see also Meissl et al 2010). The principal advantage of ring shear testing is the possibility to carry out isochoric simple shear to quasi-infinite strain.…”

“…From left to right: seismic strip chart, superposed sequence of normally sedimented muds, silts and sands (light grey) and sequences affected by submarine mass wasting (dark grey) (Data from: Flemings et al (2006),Meissl et al (2010) 41.2 Composite core log diagram of IODP Sites U1324 and U1322.…”