Time filter

Source Type

Ranasinghe D.P.L.,Tohoku University | Goto K.,Tohoku University | Takahashi T.,Kansai University | Takahashi J.,Tohoku Electric Power Co. | And 3 more authors.
Coastal Engineering | Year: 2013

Thus far various numerical models have been developed and improved to aid understanding of the sediment transport process due to tsunamis. However, the applicability of these models for the field-scale bathymetric change remains a major issue due to the scarcity of measured bathymetric data immediately before and after tsunamis. This study focuses on assessing the applicability of the sediment transport model by comparing the model results with measured bathymetry data obtained one month before and two months after the 2004 Indian Ocean tsunami at Kirinda Fishery Harbor, Sri Lanka. Obtained model results were compared with measured data along four different transects. In particular, similar to the measured data, the model reproduced the bed level change at the harbor mouth well, although it shows some discrepancy on bathymetric change along the shoreline, which is directly affected by littoral drift. Therefore, it is noted that the divergence of reproducing the local bathymetry change is due to the normal wind wave effect on measured data and the model limitations. Hence we included the wind wave effect in modeled data and the discrepancy between measured and modeled data was reduced. Furthermore, the modeled bed level change indicates a dynamic behavior in terms of the net variation during the tsunami flow, such that deposition dominates in the inflow and erosion dominates in the backflow. Both bed level variation and the suspended load concentration reveal that the large amount of eroded sediment attributable to tsunami waves was in suspended form and was deposited in the nearshore area after the water fluctuation had abated. The model results further indicate that eroded sediment at the initial depth deeper than 11. m might be brought by the incoming tsunami waves and deposited in the nearshore area where the depth is shallower than 7. m. © 2013 Elsevier B.V.


Matsumoto M.,Kyoto University | Yagi T.,Kyoto University | Hatsuda H.,Tokuyama Corporation | Shima T.,IHI Corporation | And 2 more authors.
Journal of Wind Engineering and Industrial Aerodynamics | Year: 2010

Mechanism of dry galloping of inclined cable of cable-stayed bridges is described in relation to Karman vortex mitigation. Furthermore, the role of Scruton number Sc on reduced critical velocity Vrcr of the dry galloping is investigated for practical use basing on wind tunnel tests and field observations of dry galloping or pseudo-galloping, which is classified as cable vibration with rain-state but response amplitude is abnormally large. It is verified that as far as the divergent-type of dry galloping, the design criterion subject to Sc-Vrcr proposed by FHWA (Federal Highway Administration of U.S.) seems to be reasonable for practical use, on the other hand, for the unsteady dry galloping, the Saito criterion for Sc-Vrcr diagram seems to be reasonable. © 2009 Elsevier Ltd.


Watabe Y.,Port and Airport Research Institute | Saegusa H.,Toa Corporation | Shinsha H.,Penta Ocean Construction Co. | Tsuchida T.,Hiroshima University
Proceedings of the Institution of Civil Engineers: Ground Improvement | Year: 2011

Airfoam-treated lightweight soil is lightweight and provides for the early age development of shear strength and effective utilisation of dredged soils. This paper summarises a 10 year follow-up study of the lightweight soils that were placed as backfill at the seawall in Kobe Port Island and Tokyo International airport. These two sites are the early case examples of constructions undertaken in 1996 including the recovery project after the Kobe earthquake disaster and the offshore expansion project of the Tokyo International airport. Sampling and laboratory testing were carried out to investigate the physical and mechanical properties in order to compare the initial material condition. The depth profiles of the soil parameters such as bulk density, water content, pH, calcium content, shear strength, needle penetration resistance, compressive yield stress and compression index were examined. Consequently, it was confirmed that the physical and mechanical properties of the airfoam-treated lightweight soil satisfied their required performance criteria, indicating that the lightweight soil had sufficient durability for use as geomaterial for construction in coastal areas.


Tomita T.,Port and Airport Research Institute | Takahashi K.,Penta Ocean Construction Co.
Proceedings of the Coastal Engineering Conference | Year: 2014

The 2011 Tohoku tsunami hitting Kuji port, Japan, was high whose height of 5.4 m was measured in the water area of 49.5 m deep in front of the open mouth of the port. This tsunami was accompanied by short-period waves while it propagated in the port, and then it broke in the port of 18 m deep approximately ahead on a breakwater. Since wave pressure by a tsunami with short-period waves is important for design of breakwaters according to Ikeno et al. (2006), such wave transformation and deformation should be able to be calculated for planning and designing measures to save people and reduce property loss. In this study, a non-hydrostatic mathematical model was developed to calculate tsunamis including short period waves, and validated in comparison with experimental results in which the tsunami in Kuji port was modeled.


Sasaki J.,Yokohama National University | Komatsu Y.,Penta Ocean Construction Co. | Matsumaru R.,IRM Ltd. | Wiyono R.U.A.,Yokohama National University
Journal of Coastal Research | Year: 2011

An unstructured-grid, finite-volume, 3D primitive equation coastal circulation model, FVCOM, was first slightly modified to apply to tsunami propagation and inundation problems in terms of the treatment of initial conditions. The model was applied to 2004 Indian Ocean Tsunami, focusing on propagation in Indian Ocean and inundation in Banda Aceh, Indonesia. Unstructured mesh was generated using fine Geographical Information System (GIS) datasets, covering Indian Ocean and inundation areas in Banda Aceh with a wide range of grid size from 50 km in the ocean to 5 m in Banda Aceh downtown on one grid system. The computed results are consistent with measured tidal gauges at Krabi and Kuraburi, Thailand, as well as at Ulee Lheue, Banda Aceh. Accuracy in reproducing inundation areas is highly enhanced after resolving fine structures of roads and buildings in downtown of Banda Aceh. Considering the recent progress in high resolution GIS datasets and computer resources, application of FVCOM will become an effective tool to consider management of local disaster prevention in a straightforward and easier manner.


Neupane D.,Ehime University | Yasuhara H.,Ehime University | Kinoshita N.,Ehime University | Unno T.,Penta Ocean Construction Co.
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

A grouting technique for enzymatic calcite precipitation is evaluated. Urea and calcium salt, at various concentrations, are mixed with a concentration-fixed enzyme to obtain the optimal precipitation of CaCO3. The optimally combined solution is injected into sand samples in small PVC cylinders. Then, the improvement in small-scale samples is observed. The combination, approved for small-scale tests, is further used for larger-scale tests. The porosity distribution within the soil is evaluated by sampling the treated sand at different locations. A precipitation ratio up to 80% can be obtained using a small amount of the enzyme. The results show that the in situ enzymatic CaCO3 precipitation technique may be feasible for use in larger-scale applications. A multiphysics simulator that considers the calcite precipitation reaction during the transport of the solution is adopted to predict the evolution of the porosity. The predicted porosities are compared with the measured porosities. The results show that the numerical predictions can replicate the actual changes in porosity relatively well and that the numerical model should be helpful in assuming these changes caused by the precipitated CaCO3 induced by the grouting technique examined in this work. © 2013 American Society of Civil Engineers.


Kuriyama Y.,Port and Airport Research Institute | Takahashi K.,Penta Ocean Construction Co. | Yanagishima S.,Port and Airport Research Institute | Tomita T.,Port and Airport Research Institute
Marine Geology | Year: 2014

The beach profile change caused by the 5-m-high tsunami striking the sandy Hasaki coast of Japan in 2011 was investigated using numerical simulation results and a detailed field data set including the beach profiles measured just 6. h before and three days after the tsunami attack. The magnitude of the tsunami-induced profile change had roughly the same relation to the wave energy flux as did the profile changes caused by wind-generated waves at this location. However, the mechanisms underlying the morphological changes were different. The beach profile changes due to wind waves were induced by smaller bottom stresses with longer duration, whereas the profile change due to the tsunami was induced by larger bottom stresses with shorter duration. Simulation results showed that the tsunami-induced beach profile change, including the offshore bar erosion, was largely caused by suspended sediments transported by the uprush flows of the first two tsunami waves. Compared with the amount of beach profile change at Banda Aceh due to the 2004 Indian Ocean tsunami, that at Hasaki due to the 2011 tsunami was small. The main reason for this is likely the difference in tsunami height: 5. m at Hasaki and 10. m at Banda Aceh. The second cause may be the topography of the land. © 2014 Elsevier B.V.


Shinsha H.,Penta Ocean Construction Co. | Kumagai T.,Penta Ocean Construction Co.
Geotechnical Engineering | Year: 2014

Two landfill sites were constructed on shore to dispose of dredged soil, and dredged soil was reclaimed after the placement of horizontal drains. In this manner, bulk compression of the soil has been achieved by application of vacuum consolidation method. The horizontal drain was a plastic board drain (PBD) with a width of 100 mm, a thickness of 10 mm, and a length of 117 to 171 m. The PBDs were set at both the bottom and the intermediate height of the landfill sites with a horizontal spacing of 0.8 m, and were completely overlaid with the dredged soil. By alternately placing the drain material and disposing of dredged soil at two landfill sites and applying negative pressure continuously to the sedimentary soil, it was possible to deposit an amount of sedimentary soil that corresponds to about 1.1 times the disposable volume at the landfill sites. This paper outlines the implemented construction and presents various measurement results and a settlement analysis.


Watabe Y.,Port and Airport Research Institute | Shinsha H.,Penta Ocean Construction Co. | Yoneya H.,Penta Ocean Construction Co. | Ko C.,Penta Ocean Construction Co.
Soils and Foundations | Year: 2014

The dredged soil dumped into a reclamation facility is generally heterogeneous. If the reclamation is executed using hydraulic transportation through pipes, large particles will be deposited around their outlets, and fine particles will be deposited apart from those outlets, resulting in significant grain size segregation. Therefore, ground improvement by applying a preload or vacuum to the dredged soil deposit with prefabricated vertical drains (PVDs) may result in an unexpected differential settlement. In the present study, partial sandy layers in a dredged soil deposit were identified as three-dimensional information using the penetration resistance of the mandrel in the PVD installation, which was recorded as dense information for a wide region. It was clarified that the depth profile of the penetration resistance of the mandrel in the PVD installation was useful for investigating the soil stratigraphy, because it is closely related to the depth profile of the tip resistance in cone penetration tests (CPTU). The relative penetration resistance, defined as the penetration resistance eliminating the data trend that reflects the effects of the overburden stress, shear strength, sleeve friction and buoyance, is useful for identifying the partial sandy layers in a dredged soil deposit. A classification equation was proposed for identifying the partial sandy layers. Firstly, the depth profile without the sandy layer was approximated, and then the threshold value of 1.0 MN/m2 was used to identify the partial sandy layer. To verify the availability of this proposed method, the depth profiles were compared with the results of CPTU tests. In addition, the predicted settlement, calculated on the basis of the stratigraphy obtained using the penetration resistance of the PVDs, was compared with the ground surface profile leveled after vacuum consolidation. © 2014 Japanese Geotechnical Society.


Neupane D.,Ehime University | Yasuhara H.,Ehime University | Kinoshita N.,Ehime University | Ando Y.,Penta Ocean Construction Co.
Soils and Foundations | Year: 2015

This study discusses the possible application of enzyme mediated calcite precipitation, EMCP, as a soil-improvement technique. It explains the experimental works on this EMCP technique. The first part of this paper addresses the different methods for quantifying the amount of calcite precipitated within sand. Two methods, namely, the thermal decomposition method and the CO2 volume evaluation method, are examined. These methods serve to evaluate the calcite distribution within the treated sand. The second part of this paper explains the experimental procedures and the results of drum-can experiments. Homogenous sand specimens, with a diameter of 57 cm and a height of 60 cm, are prepared inside a steel drum-can. A grout solution, comprising urea, urease, and CaCl2, is injected into the centre of the sand specimens. Subsequently, the improved samples within the specimens are collected and their compressive strength is evaluated. The maximum measured unconfined compressive strength is 380 kPa. An attempt is made to relate the improved mechanical properties of EMCP-treated sand to the amount of mineralized carbonate. The obtained calcite-strength relation is found to be in close agreement with the relation obtained in previous literature. © 2015 Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

Loading Penta Ocean Construction Co. collaborators
Loading Penta Ocean Construction Co. collaborators