Seabed Liquefaction Research Articles

Wave Prediction Using Neural Networks at New Mangalore Port along West Coast of India

Estimation of wave parameters is of great importance in coastal activities such as design studies for harbour, inshore and offshore structures, coastal erosion, sediment transport and wave energy estimation. Traditional methods like semi empirical formulations and numerical models have disadvantages of excessive data requirement, time consumption and are tedious to carry out.Artificial Intelligent methods like ANN (Artificial Neural Network) are powerful and flexible modeling tool is being widely used in coastal engineering field since last two decades for solving various problems related to time series forecasting of waves and tides; prediction of sea-bed liquefaction and scour depth; and estimation of design parameters of coastal engineering structures. It imbibes the qualities of exploiting non-linearity, adaptability to adjust free parameters by mapping input output data sets using various learning algorithms and fault tolerance.Using input and output information, intelligent systems enabled to estimate the hidden law behind the information and to find their relations among them. In the present study attempt has been made to predict waves at New Mangalore Port Trust (NMPT) located along the west coast of India using Feed Forward Back Propagation (FFBP) with LM algorithm and a recurrent network called Non-linear Auto Regressive with exogenous input(NARX) network. Field data of NMPT has been used to train and test the network performance, which are measured in terms of mean square error (mse) and correlation coefficient (r). Effect of network architecture on the performance of model has been studied.Correlation coefficient is found to be 0.94 in case of NARX predictions indicating better performance than FFBP network whose ‘r’ value is 0.9. It was found that for time series prediction NARX network outperform FFBP network not only in terms of accuracy but also in terms of time required for computation.

Effects of wave-induced seabed liquefaction on sediment re-suspension in the Yellow River Delta

This paper presented the results of wave flume experiments for the process of a silty sediment bed responded to wave action. Silty sediment was sampled from modern Yellow River Delta. In coastal areas, seabed liquefaction and sediment re-suspension were the most significant hydrodynamic processes the seabed sediment presented under wave action. However, few studies have focused on the internal response of sediment under wave action with regard to its role in liquefaction and sediment re-suspension. In this study, four wave height scenarios (5cm, 7cm, 10cm and 18cm) were tested. Results indicated that the movements of the suspended sediments were dominated by the re-suspension of surface sediment erosion at the initial stage of wave action, whereas the suspended sediments were transported from the internal seabed sediment upward due to wave-induced liquefaction and seepage at a later stage. The observations confirmed that waves enhanced sediment re-suspension by liquefying the soil bed through excess pore pressure accumulations, not simply by excess shear stress.

Wave and current induced seabed response around a submarine pipeline in an anisotropic seabed

A better understanding of the phenomenon of wave–seabed-structure interactions is essential for the evaluation of the liquefaction of seabed foundation under dynamic loading in the ocean environments. However, only a few investigations have been conducted for the cross-anisotropic seabed under wave pressure and marine structures, despite the fact that most seabeds are anisotropic medium. Furthermore, most previous numerical models for Biot's consolidation theory were only considered wave loading. In this study, based on Biot's partly dynamic poroelastic theory (“u-p” approximation), a two-dimensional FEM seabed model is adopted to investigate the wave and current induced seabed response around a submarine pipeline. The third-order solution of wave-current interactions is used to determine the dynamic pressure acting on the seabed. Verification of the proposed model is performed against the previous experimental data and analytical result. With the proposed numerical model, the effects of wave, current and seabed characteristics, such as Poisson's ratio, Young's modulus, degree of saturation, and pipeline buried depth on the wave-induced seabed response will be examined. Then, the wave-current induced seabed liquefaction is also discussed. The numerical results demonstrate significant effects of anisotropic soil behavior on seabed liquefaction.

3-D Liquefaction Potential Analysis of Seabed at Nearshore Area

In this research, we discussed about the wave induced seabed liquefaction at nearshore based on the viewpoint of marine geotechnical engineering. The behaviors of seabed sand under wave loading were evaluated by experiments carried out in the Chien's cyclic triaxial testing system (type Ⅱ). Different loading periods, effective confining pressure and relative densities affected the liquefaction resistance of seabed sand that we sampled at northeastern coast in Taiwan. Furthermore, this study proposed the 3-D evaluation method of seabed liquefaction at Yi-Lan nearshore in case that combined the liquefaction resistance of seabed sand and Nearshore Spectral Wind- wave (NSW) model. The new 3-D method could evaluate the distribution and thickness of wave-induced seabed liquefaction at nearshore area.