Instantaneous Liquefaction Research Articles

Wave-induced dynamic response and instability of seabed around caisson breakwater

In this study, standing wave-induced dynamic response and instability of seabed around a caisson breakwater are investigated. A seabed-rubble-caisson breakwater system is modeled using finite elements. The dynamic response of the porous seabed-rubble foundation is assumed to be governed by the Biot’s equations of coupled flow and deformation. Three possible formulations (fully dynamic, partly dynamic and quasi-static) are considered with respect to the inclusion of inertial terms associated with the motion of fluid and solids. The response is presented in terms of stress and pore pressure distributions at three locations underneath the breakwater. The instability of seabed and rubble mound due to instantaneous liquefaction is also studied. The effects of seabed and wave parameters and the effect of inertial terms on the standing wave-induced dynamic response and instability of the system are investigated through a set of parametric studies. Analyses show that quasi-static and partly dynamic formulations yield similar results while the fully dynamic formulation provides different response. The results from different formulations suggest the use of all inertial terms (fully dynamic formulation), providing the most complete solution and the least conservative response.

Physical agglomeration behavior in preparation of cellulose‐N‐methyl morpholine N‐oxide hydrate solutions by simple mixing

AbstractThe different melting temperatures of N‐methyl morpholine N‐oxide (NMMO) hydrates in the cellulose–NMMO hydrate solution may be explained by the rather different crystal structures of NMMO hydrates, which are determined by the amount of the hydrates. The preparative process of cellulose–NMMO hydrate solution may result in cellulose structural change from cellulose I to cellulose II, depending on the amount of the hydrate. Mixtures of cellulose and NMMO hydrate in a blender was changed from the granules to slurry with increasing mixing time at 60–70°C, which is below the melting point of the NMMO hydrate. In the case of 15 wt % cellulose–NMMO hydrate granules, which were made by mixing for 20 min, the melting points of various NMMO hydrates were obtained as 77.8°C (n = 0.83), 70.2°C (n = 0.97), and 69.7°C (n = 1.23), respectively, depending on the hydrate number. However, the melting points of cellulose–NMMO hydrate slurry and solution were shifted lower than those of cellulose granules, while the mixing time of slurry and solution are 25 and 35 min, respectively. These melting behaviors indicate instantaneous liquefaction of the NMMO hydrate and the diffusion of the NMMO hydrate into cellulose during mixing in a blender. When cellulose was completely dissolved in NMMO hydrate, the crystal structure of cellulose showed only cellulose II structure. In the cellulose–NMMO products of granules or slurry obtained by high‐speed mixing, which is a new preparation method, they still retained the original cellulose I structure. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1687–1697, 2004

Analyse de la liquéfaction et du comportement non drainé des sables du delta de Kenamu (Projet ADFEX)

Jointly sponsored by France, Norway, and Canada, the ADFEX project (Artic Delta Failure Experiment) aims at triggering a full-scale submarine slide. For that purpose, a delta is destabilized by blasting to induce instantaneous liquefaction of the delta front. The selected site is the delta of Kenamu River at Melville Lake (Labrador), located approximately 40 km northeast of Goose Bay. The delta sediments are angular fine silty sands constituted mainly of quartz. A series of consolidated isotropically and undrained triaxial tests was performed on specimens of reconstituted loose sands to establish the boundaries between the contracting and dilating behaviours (steady state line or F line) and the upper and lower limits of the boundaries within the bidimensional diagram void ratio – mean effective stress. A soil state above this boundary region constitutes a necessary condition to liquefaction. The results of the triaxial tests are used to evaluate the liquefaction potential of Kenamu delta. Key words : liquefaction, sand, steady state, triaxial test, undrained, delta.