Liquefaction potential of coastal slopes induced by solitary waves

Tsunami runup and drawdown can cause liquefaction failure of coastal fine sand slopes due to the generation of high excess pore pressure and the reduction of the effective over burden pressure during the drawdown. The region immediately seaward of the initial shoreline is the most susceptible to tsunami-induced liquefaction failure because the water level drops significantly below the still water level during the set down phase of the drawdown. The objective of this work is to develop and validate a numerical model to assess the potential for tsunami-induced liquefaction failure of coastal sandy slopes. The transient pressure distribution acting on the slope due to wave runup and drawdown is computed by solving for the hybrid Boussinesq—nonlinear shallow water equations using a finite volume method. The subsurface pore water pressure and deformation fields are solved simultaneously using a finite element method. Two different soil constitutive models have been examined: a linear elastic model and a non-associative Mohr–Coulomb model. The numerical methods are validated by comparing the results with analytical models, and with experimental measurements from a large-scale laboratory study of breaking solitary waves over a planar fine sand beach. Good comparisons were observed from both the analytical and experimental validation studies. Numerical case studies are shown for a full-scale simulation of a 10-m solitary wave over a 1:15 and 1:5 sloped fine sand beach. The results show that the soil near the bed surface, particularly along the seepage face, is at risk to liquefaction failure. The depth of the seepage face increases and the width of the seepage face decreases with increasing bed slope. The rate of bed surface loading and unloading due to wave runup and drawdown, respectively, also increases with increasing bed slope. Consequently, the case with the steeper slope is more susceptible to liquefaction failure due to the higher hydraulic gradient. The analysis also suggests that the results are strongly influenced by the soil permeability and relative compressibility between the pore fluid and solid skeleton, and that a coupled solid/fluid formulation is needed for the soil solver. Finally, the results show the drawdown pore pressure response is strongly influenced by nonlinear material behavior for the full-scale simulation.     

Recreational boat noise level evaluation

Recreational boats are constantly undergoing modifications and improvements in design, construction materials, and equipment. The boat builder mission is supply customers with a product with better quality, safety and onboard comfort. Onboard comfort should be evaluated along several points. Seakeeping is especially critical on long trips or operations in regions where harsh sea conditions occur. Over the years much attention has been given to boat behavior underway at sea. Recently onboard noise level has become a significant element of comfort and navigation safety. With high onboard noise a boater is unable to detect other boat whistles, horns and calls for help. This becomes a critical problem when sailing in fog and at night. Maintaining the internal noise level within limits is important. In order to address this noise problem, the paper presents a review of existing guidelines and the authors' proposal for Boat Noise Evaluation (BNE) procedure for recreational powerboats. This procedure has been used in a number of boat trials. The use of this procedure is discussed along with representative boat noise level results and a comparison with the acceptable values for passenger comfort and safety.     

Landscape evolution and geodynamic controls in the Gulf of Cadiz (Huelva coast, SW Spain) during the Late Quaternary

The coastal evolution of the El Abalario area (Huelva, southern Spain) during the Late Pleistocene and Holocene is reinterpreted after a refinement of the available geochronology by means of optically stimulated luminescence (OSL) dating. New data come from the analysis of soft sediment deformation, palaeosols, geomorphological mapping, and published seismic surveys on the onshore and offshore Gulf of Cadiz.The present structure of El Abalario dome resulted from the complex interaction of littoral-catchment processes and sea-level changes upon an emergent coastal plain, conditioned by the upwarping of the underlying Pliocene–Pleistocene prograding deltaic sequence. Upwarping is probably related to escape of over-pressurized fluids, accompanied by dewatering, prior to (?) and during OIS (Oxygen Isotopic Stage) 5. Continued upwarping produced the large NW–SE gravitational fault of Torre del Loro (TLF) in the southwestern flank of the dome, roughly parallel to the present coastline during OIS 5–OIS 4. The resulting escarpment favoured the accumulation of aeolian sand dunes (units U1, U2, and U3) from OIS 5 to early OIS 1. Unit U1 (OIS 5) ends upwards in a supersurface with a thick weathering profile that suggests moist and temperate climatic conditions. Unit U2 accumulated mainly during OIS 4 and OIS 3 with prevailing W/E winds. The supersurface between U2 and U3 records a part of OIS 2, with relative low sea level. Sedimentation of unit U3 took place during the Last Deglaciation (radiocarbon and OSL ages) with prevailing W/SW winds, under a temperate moist climate, that became more arid towards the top (Holocene). A major supersurface with an iron crust-like layer (SsFe) developed during the Holocene Climatic Optimum (OIS 1) under wetter and more temperate conditions than before, fossilizing the TLF. The supersurface is covered by younger aeolian dunes (U4, U5, U6, and U7) transported by W–SW winds since the Late Neolithic–Chalcolithic cultural period (5.0 ky cal BP).     

Reduction of jack-up and crane vessel resistance and bow swamping

A large bow wave forms when blunt-shaped vessels like self-propelled jack-up crane vessels (liftboats) operate at high speeds. Above a critical speed, this bow wave spills over the bow causing swamping. To investigate this phenomena, towing tank tests of a 1/25 scale model liftboat hull were done over a speed range of 3–8 kn. The test showed above 4 kn the bow wave formed and the vessel trimmed by the bow. At speeds above 8 kn the bow wave spilled over the bow (swamping). To cancel this critical bow wave a vertical bow plate was fitted ahead of the liftboat bow. This bow plate reduced the bow wave formation and achieved a 10–15% reduction in the towing resistance. The wave cancellation bow plate can reduce the liftboat power or increase its liftboat speed and operating range.     

The impacts of hysteresis on variably saturated hydrologic response and slope failure

This investigation employs 3D, variably saturated subsurface flow simulation to examine hysteretic effects upon the hydrologic response used to drive unsaturated slope stability assessments at the Coos Bay 1 (CB1) experimental catchment in the Oregon Coast Range, USA. Slope stability is evaluated using the relatively simple infinite slope model for unsaturated soils driven by simulated pore-water pressures for an intense storm that triggered a slope failure at CB1 on 18 November 1996. Simulations employing both hysteretic and non-hysteretic soil–water retention curves indicate that using either the drying soil–water retention curve or an intermediate soil–water retention curve that attempts to average the wetting and drying retention curves underestimates the near-surface hydrologic response and subsequently the potential for slope failure. If hysteresis cannot be considered in the hydrologic simulation, the wetting soil–water retention curve, which is seldom measured, should be used for more physically based slope stability assessment. Without considering hysteresis or using the wetting soil–water retention curve, the potential for landsliding in unsaturated materials may be underestimated and a slope failure could occur when simulations predict stability.