Influences of Nutrient Outwelling from the Mangrove Swamp on the Distribution of Phytoplankton in the Matang Mangrove Estuary, Malaysia

Distributions of dissolved nutrients and Chl. a were investigated in the Sangga Besar River Estuary in the well-managed Matang Mangrove Forest in West Malaysia. In the estuary, spring tide concentrations of ammonium, silicate and phosphate were higher than those in the neap tide, which suggests that these nutrients are flushed from the mangrove area by the inundation and tidal mixing of the spring tide. Ammonium comprised over 50% of the dissolved inorganic nitrogen in the spring tide, while nitrite tended to dominate in the neap tide, indicating the predominance of nitrification inside the estuary in neap tides. Nutrient concentrations in the creek water were higher than those of estuarine water, indicating the nutrient outwelling from the mangrove swamp and ammonium regeneration from mangrove litter in the creek sediments. The maximum concentration of Chl. a in spring tides reached 80 g/l while it was below 20 g/l in the neap tides. These variations in the phytoplankton biomass and nutrients probably reflect the greater nutrient availability in the spring tide due to outwelling from the mangrove swamp and creek.     

Shearing characteristics of SCP-inserted clay specimens in triaxial compression test

Sand compaction piles (SCPs) have been widely applied to the construction on the soft ground for decades, due to not only the acceleration of the consolidation but also the enhancement of strength and stiffness of ground. However, physical behaviors of SCP-improved ground have not been clearly unveiled due to complex response of two distinct materials, compacted sand and soft clay, which are having quite different mechanical characteristics. Therefore, in this study, the mechanical characteristics of SCP composite ground were investigated via triaxial compression tests on SCP-inserted clay specimens. Tests were performed elaborately with four specimens with different replacement ratios. Based on the comparisons of consolidation and shearing behaviors of tested SCP-inserted clay specimens, the SCP effects on the stiffness and strength are also investigated. Even though the SCP-inserted clay specimens show stronger and stiffer behaviors than clay-only specimens, the effects vary on strength, stiffness, and volume change with regard to the applied replacement ratios.     

Numerical Studies on Piled Gravity Base Foundation for Offshore Wind Turbine

This study aims to investigate a hybrid gravity base foundation to support offshore wind tower. A new hybrid gravity base foundation considered in this study has five component piles, referred to as ‘piled gravity base foundation’. The three-dimensional finite element analyses were carried out for the piled gravity base foundation subjected to a combined load with a lateral load and overturning moment. The parametric analyses were undertaken varying the loading height and direction, the rigidity of the piled gravity base foundation, the field soil layers, and the clay strength. Overall, the response of the piled gravity base foundation was significantly influenced by the interaction between the cone base piles and the surrounding soil. The increased strength of the soil led to a significant reduction of the pile and gravity base foundation responses, in terms of the bending moments, axial forces, lateral displacements, and rotations.     

Discharge prediction using hydraulic characteristics of mean velocity equation

Discharge is an important factor in river design for water utilization, water control and hydraulic structures; therefore, an accurate estimation of the discharge is required. At present, a rating curve depicting the relationship between a stage and discharge is used to calculate the discharge from river systems. Although the rating curve has an advantage in that it can predict and use the discharge during the flood season in which the measurement is difficult, there is room for improvement as it does not reflect the hydraulic characteristics of rivers. Therefore, in this study, discharge was predicted using the convenient calculation method with empirical mediating variables of the Manning and Chezy equations which were proposed by the author’s previous research as a new methodology for estimating discharge in an open channel. This was proven, based on the data measured in a meandering open channel system in a lab at the Mississippi River in the US and at the Columbia Del Dique Canal, and an accuracy level at a coefficient of 0.8 was demonstrated. Thus, this method, which reflects the hydraulic characteristics and predicts the discharge in a simple manner, is expected to be convenient in practice.     

The effect of mineralogy on the mobility of heavy metals in mine tailings: a case study in the Samsanjeil mine,Korea

This study examined the chemical speciation and mobility of As and heavy metals in a tailings impoundment in Samsanjeil mine located in Gosung, Korea, as well as the factors affecting them. XRD, SEM, and 5-step sequential extraction were used to examine the samples at two sampling sites (NN and SN sites). The pH of the tailings decreased with increasing depth at the NN site (from 7.2 to 2.8), whereas no significant differences were observed at the SN site (8.1–8.8). The samples at the SN site showed a larger amount of calcite than those at the NN site, indicating that calcite plays an important role buffering the pH in the study sites. Jarosite was found only at the lower part of the NN site, where calcite was not found. The mineralogical observation of jarosite and calcite was also confirmed by SEM. The concentrations of As and heavy metals in the tailings were as follows: Cu > As > Zn > > Pb > Co > Cr > Ni > Cd. The total concentrations of Ni, Zn, Co, and Cd were higher at the SN site than those at the NN site. On the other hand, the concentrations of As and Cr existing as oxyanions were higher at the NN site, which can be explained by the mobility changes of those elements affected by pH variations. At the NN site, the fractions of heavy metals bound to the Fe/Mn oxides, except for As and Cr, decreased, and Cu, Zn, and Co showed an increasing fraction of exchangeable metals with increasing depth. This suggests that the pH and resulting surface charge of minerals, such as goethite and jarosite, are the dominant factors controlling the chemical speciation of metals. These results highlight the importance of mineralogy in controlling the mobility and possible bioavailability of heavy metals in tailings.     

Hybrid continuum–discrete simulation of granular impact dynamics

Acta Geotechnica - Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics....     

Stability Study of a Tide Embankment Subjected to Sea Level Variations Using Centrifugal Model Tests

To investigate the behavior of dredged-sea-sand fill compacted inside tide embankments with a damaged geosynthetic mat, centrifugal model tests and numerical simulation were conducted, both considering variations in sea level. The results from the three centrifugal model tests demonstrate that the subsidence of the dredged-sea-sand fill inside tide embankments with a damaged geosynthetic mat was strongly affected by the loss of dredged-sea-sand into the filter layers with large particles and a decrease in the bearing capacity of the filter layers with small particles. In addition, a comparison of the test and simulation results confirms that the loss of sand into the filter layer and the subsidence of the dredged-sea-sand fill were well reproduced by the numerical simulation.     

Stress-induced evolution of anisotropic thermal conductivity of dry granular materials

Various factors, such as the volumetric fraction of constituents, mineralogy, and pore fluids, affect heat flow in granular materials. Although the stress applied on granular materials controls the formation of major pathways for heat flow, few studies have focused on a detailed investigation of its significance with regard to the thermal conductivity and anisotropy of the materials. This paper presents a numerical investigation of the stress-induced evolution of anisotropic thermal conductivity of dry granular materials with supplementary experimental results. Granular materials under a variety of stress conditions in element testing are analyzed by the three-dimensional discrete element method, and quantitative variations in their anisotropic effective thermal conductivity are calculated via the network model and conductivity tensor measurements. Results show that the directional development of contact area and fabric under anisotropic stress conditions leads to the evolution of anisotropy in thermal conductivity. The anisotropy induced in thermal conductivity by shear stress is higher than that induced by compressive stress because shear stress causes more significant changes in microstructural configurations and boundary conditions. The shear-stress-induced evolution of anisotropy between principal thermal conductivities depends on dilatancy as well as shearing mode, and the shear-driven discontinuity localizes the conductivity. Factors involved in the stress-induced evolution and their implications on the thermal conductivity characterization are discussed.     

Characteristics of the eddy caused by Izu-Oshima Island and the Kuroshio branch current in Sagami Bay,Japan

Direct current measurements of the branch current of the Kuroshio intruding into Sagani Bay were carried out during 1989–1990 in order to clarify the frequency characteristics of the eddies in the lee of Izu-Oshima Island, which are well recognized as cold water mass produced by upwelling. Satellite and ADCP (Acoustic Doppler Current Profiler) data indicated that current velocity in the eddy fluctuates with periods of 2–4 days and 6–8 days.When the Kuroshio branch current intruding into Sagami Bay from the western channel is weak and its velocity at the depth of 400 m is approximately 10 cm s^–1, the 6–8 day period fluctuation is dominant. On the other hand, when the branch current strongly intrudes from the western channel with a velocity of approximately 20 cm s^–1, the 2–4 day period fluctuation dominates. The relationship between the periods and velocities agrees well with theory based on laboratory experiments for a flow of a homogeneous fluid past a circular obstacle. These periods correspond to the time scale of appearance of the eddy caused by the intrusion of the Kuroshio branch current into Sagami Bay and Izu-Oshima Island.