Penta Ocean Construction Co.

Penta, Japan

Penta Ocean Construction Co.

Penta, Japan
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Sugimoto H.,Penta Ocean Construction Co. | Moriya Y.,Penta Ocean Construction Co. | Ogasawara T.,Penta Ocean Construction Co.
2017 IEEE OES International Symposium on Underwater Technology, UT 2017 | Year: 2017

In the midst of growing concern by labor shortage, there is an urgent and major need for efficient maintenance and effective management of aging infrastructure. Inspection and investigation of large underwater structures such as dam embankments with depth of more than 40m, offshore and port structures by human divers is the challenging task from the viewpoint of safety and efficiency. In this paper we have participated in the event offered by the Ministry of Land, Infrastructure and Transport, a symposium for, The Next Generation Social Infrastructure Robotic Inspection and have obtained the field verification results by using Underwater Inspection Robots in inspecting dam structures. © 2017 IEEE.

Toshinari Y.,Tokyo Institute of Technology | Matsuda S.,Tokyo Institute of Technology | Kitazume M.,Tokyo Institute of Technology | Nguyen B.,Penta Ocean Construction Co.
Geotechnical Special Publication | Year: 2017

Column type deep mixing of improved ground has frequently been used to increase stability of embankments constructed on a soft ground. Model tests and numerical analyses have been carried out to study the behavior and failure pattern of improved ground subjected to embankment load, where the sliding, overturning and bearing capacity failures of the improved ground were studied in the external stability, the shear and bending failures of the deep mixing columns were studied in the internal stability. Almost all studies investigated the stability of the improved ground sitting on a horizontal foundation. However the stability of the improved ground sitting on an inclined foundation has not been well studied. In this study, the external stability of DMM columns on an inclined foundation was investigated by centrifuge model tests. The model test results were compared with the finite element analyses. As a result, the experiment and finite element analyses revealed that the columns showed a rotational failure pattern and the stability of improved ground was almost constant irrespective of the inclination of foundation layer. © ASCE.

Nguyen B.,Penta Ocean Construction Co. | Takeyama T.,Kobe University | Kitazume M.,Tokyo Institute of Technology
Geotechnical Special Publication | Year: 2017

When the deep mixing columns were used to support embankment slope, the columns may fail under either the internal or the external failure pattern, dependent on the strength of columns, soil condition, and loading condition. A shallow layer, produced by shallow mixing method, was proposed to fix and reinforce these isolated columns. In this study, the centrifuge model tests were carried out to simulate the embankment construction on the soft ground, improved by the columns and the shallow layer. The effect of the shallow layer and column strength on increasing the embankment stability can be addressed from the model tests. The failure of isolated columns was compared to that of columns with the reinforcement of shallow layer in terms of internal stability. In addition, by using the test data simple calculations based on limit equilibrium were also carried out to access the failure patterns of column in both internal and external stabilities. © ASCE.

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.

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.

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.

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