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Construction Inc. and Fudo Tetra Corporation | Date: 2014-03-12

An improved method of limestone and sandy soil compaction comprising a first tamping session using a 1010 vibro tamper plate timed for about 90 seconds followed by at least 4 days of settling. A second tamping session using the 1010 vibro tamper plate timed for about 120 seconds followed by at least 4 days of settling. A third tamping session using a 77 vibro tamper plate for about 90 seconds followed by about 6 days of settling. The disclosed method provides an improvement over deep dynamic compaction (DDC) by providing a soil compaction method that has a higher production rate than DDC, reduces the vibration and noise level as compared to the DDC and thereby lessens the impact on neighboring structures.

Hanzawa M.,Fudo Tetra Corporation | Matsumoto A.,Fudo Tetra Corporation | Tanaka H.,Tohoku University
Earth, Planets and Space | Year: 2012

Detached breakwaters, made with wave-dissipating concrete blocks such as Tetrapods, have been widely applied in Japan, but the effectiveness of such kinds of detached breakwaters on tsunami disaster prevention has never been discussed in detail. A numerical wave flume called CADMAS-SURF has been developed for advanced maritime structure design. CADMAS-SURF has been applied mainly to ordinary wave conditions such as wind waves, and little attempt has been made for expanding its application to tsunami waves. In this study, the applicability of CADMAS-SURF for evaluating the effectiveness of detached breakwaters on a solitary tsunami wave reduction is investigated by comparing the calculated results with those from hydraulic experiments. First, the effectiveness of a detached breakwater on the reduction of wave height and wave pressure was confirmed both by hydraulic experiments and numerical simulations. Finally, CADMAS-SURF has been found to be a useful tool for evaluating the effects of detached breakwaters on tsunami wave height and pressure reduction, as a first step in a challenging study. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

Yasuda S.,Tokyo Denki University | Harada K.,Fudo Tetra Corporation | Ishikawa K.,Tokyo Denki University | Kanemaru Y.,Kyushu Branch
Soils and Foundations | Year: 2012

The 2011 Great East Japan Earthquake caused the severe liquefaction of reclaimed lands in the Tokyo Bay area, from Shinkiba in Tokyo through Urayasu, Ichikawa and Narashino Cities to Chiba City. However, the reclaimed lands that had been improved by the sand compaction pile method, the gravel drain method or other methods did not liquefy. The reclaimed lands that did liquefy had been constructed after around 1966 with soil dredged from the bottom of the bay. The dredged and filled soils were estimated to have been liquefied by the earthquake. Seismic intensities in the liquefied zones were not high, although the liquefied grounds were covered with boiled sand. Most likely it was the very long duration of the main shock, along with the large aftershock that hit 29 min later, which induced the severe liquefaction. Sidewalks and alleys buckled at several sites, probably due to a kind of sloshing around of the liquefied ground. Moreover, much sand boiled from the ground and the ground subsided significantly because the liquefied soil was very fine. Many houses settled notably and tilted. In Urayasu City, 3680 houses were more than partially destroyed. Sewage pipes meandered or were broken, their joints were extruded from the ground, and many manholes were horizontally sheared. This remarkable damage may also have occurred due to the sloshing around of the liquefied ground. © 2012 The Japanese Geotechnical Society.

Okamura M.,Ehime University | Takebayashi M.,Toa Corporation | Nishida K.,Fudo Tetra Corporation | Fujii N.,Chiyoda Corporation | And 4 more authors.
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2011

Desaturation of ground by air injection attracts considerable attention in recent years as an innovative technique for a liquefaction countermeasure. Several research programs were conducted in laboratories regarding the related topics. This paper describes an in situ air-injection test that aims to examine the effectiveness of the air injection to desaturate ground and the validity of observation techniques to monitor the evolution of the unsaturated zone. In the test, air was injected from an air injector deployed in a targeted saturated-sand layer at a depth of 6 m. Observations revealed that the air-flow rate increased linearly with increasing air-injection pressure and the desaturated zone was generated within 4 m from the injection point. A 3-dimensional electric resistivity tomography technique was effective for evaluation of the desaturated zone. The degree of saturation of the in situ soil was observed by using high quality undisturbed samples obtained by the ground freezing method. The degree of saturation ranged from 68-98%, which was low enough to almost double the liquefaction resistance of the soil at the site. Numerical analyses were also conducted with a gas-liquid two-phase flow simulator to describe the evolution of the soil desaturation. Qualitatively, predictions show a relatively good agreement with the in situ measurements of the 3D electric resistivity tomography and are quantitatively compatible with the in-field degree of saturation measured indirectly by using the frozen soil samples. Actual liquefaction resistance was evaluated utilizing the undisturbed samples by conducting a triaxial test under cyclic shear conditions, which revealed that desaturated samples were indeed less susceptible to liquefaction compared with the fully saturated samples. © 2011 American Society of Civil Engineers.

Yasuda S.,Tokyo Denki University | Harada K.,Fudo Tetra Corporation
NCEE 2014 - 10th U.S. National Conference on Earthquake Engineering: Frontiers of Earthquake Engineering | Year: 2014

In Japan, many remediation methods against liquefaction have been developed since the 1964 Niigata Earthquake, which caused severe damage to structures due to liquefaction. The methods are classified into two categories: ground treatments to prevent liquefaction, and measure that strengthen structures to prevent or minimize damage if the ground liquefies. The remediation methods have been applied to many kinds of structures, such as oil tanks, quay walls, bridges and buildings. The effectiveness of ground treatments to prevent liquefaction has been proved during past earthquakes. However, a new problem was raised during the 1995 Hyogoken-nambu (Kobe) Earthquake because recorded accelerations were far greater than the design acceleration. Then, studies on the adoption of performance-based design started. The 2011 Great East Japan (Tohoku) Earthquake demonstrated the need for a new concept of measures to prevent liquefaction in areas encompassing houses, roads and lifelines. One of these measures is lowering the ground water table. The applicability of this measure has been confirmed by in-situ tests and analyses, and lowering work started in several cities in 2013.

Rasouli R.,Penta Ocean Institute of Technology | Rasouli R.,University of Tokyo | Towhata I.,University of Tokyo | Akima T.,Fudo Tetra Corporation
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2016

The earthquakes of 2010 and 2011 in New Zealand and Japan caused significant liquefaction-induced damage in both countries. Unlike previous experiences in which damage to infrastructures was the main concern of people and engineers, vast distortion of private houses caused serious problems for society. The objective of researchers and engineers after these two events was to propose technicallyreliable and economically-affordable mitigation measures to people. This paper examines the efficiency and performance of installing various configurations of drains, and their combination with sheet-pile walls in different groundwater levels. The results revealed that unless there is perfect nonliquefied ground under a building's foundation, settlement of the structure cannot be reduced significantly. In this regard, preventing liquefaction in shallower depths has crucial importance. It also was found that using sheet-pile walls equipped with drains enhanced individual performance of both drains and sheet-piles. © 2016 American Society of Civil Engineers.

Rasouli R.,University of Tokyo | Towhata I.,University of Tokyo | Hayashida T.,Fudo Tetra Corporation
Physical Modelling in Geotechnics - Proceedings of the 8th International Conference on Physical Modelling in Geotechnics 2014, ICPMG 2014 | Year: 2014

Subsidence of surface structures has been seen during earthquakes in liquefaction prone areas since many years ago. To date no reliable measure against this problem with reasonable cost has been proposed to people. In this study a series of 1-g shaking table tests have been conducted to evaluate performance of possible mitigations. These experiments concerned lowering of ground water level and installation of sheet-pile walls around the foundation. As expected from case histories records, lowering of ground water level could reduce subsidence of model structure. It is found out that installing sheet-pile walls along with lowering water level can stop settlement completely. In contrast, using sheet-pile walls with open spaces (for cost reduction) between sheets can even increase the magnitude of settlement. Other interesting finding of this series of experiments is the role of formation of water film in post-shaking subsidence of structures. © 2014 Taylor & Francis Group.

Rasouli R.,University of Tokyo | Towhata I.,University of Tokyo | Hayashida T.,Fudo Tetra Corporation
Soil Dynamics and Earthquake Engineering | Year: 2015

Settlement of surface structures, which is particularly a private house, due to subsoil liquefaction is not a new issue in geotechnical engineering. It has been happening during earthquakes in liquefaction-prone areas since many years ago. However, to date no reliable measure against this problem with reasonable cost has been proposed to people. In this paper, results of a series of 1-g shaking table tests which have been conducted to evaluate performance of a possible mitigation against this problem are presented. The proposed mitigation herein is installation of sheet-pile walls around the foundation. In order to reduce the cost of mitigation, sheet-piling with gap and half-length sheet-piling were examined. The experiments were conducted in different ground water levels. It is found out that installing sheet-pile walls in relatively low ground water level can stop settlement of structures completely. Sheet-piling with gaps delays initiation of settlement but it may increase the ultimate settlement of structure. In addition, it is found that formation of a water film under the building[U+05F3]s foundation is the governing mechanism of post-shaking settlement of structures. © 2015 Elsevier Ltd.

Nozu M.,Fudo Tetra Corporation | Sakakibara M.,Fudo Construction Inc. | Matsushita K.,Fudo Tetra Corporation
15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2015: New Innovations and Sustainability | Year: 2015

At the runway expansion project in the Fort Lauderdale-Hollywood International airport in Florida (FLL project), there are complicated geotechnical issues that lots of cavities in the limestone-loose sand mixed ground are existing in the shallow area. The Broward County Aviation Department (BCAD), the owner of the project, has required to collapsing the cavities and compacting the runway foundation to secure the take-off and landing of aircrafts. Mammoth Vibro-Tamper (MVT) was proposed and accepted as the alternative to the originally specified Deep Dynamic Compaction (DDC) for the runway with its length of 2.4km and area of 477,000 m2. In this report, the shallow compaction effect and vibration reduction effects by MVT are presented in comparison with the DDC.

Mitsui J.,Fudo Tetra Corporation | Matsumoto A.,Fudo Tetra Corporation | Hanzawa M.,Fudo Tetra Corporation | Nadaoka K.,Tokyo Institute of Technology
Coastal Engineering Journal | Year: 2016

This paper presents a practical design method for armor units to cover a rubble mound at the rear side of a caisson breakwater against tsunami overflow. In this method, the overflow depth of tsunami is used to represent the external force. This enables the estimation of the required mass of the armor units to be done more robustly and easily than in the conventional method based on the flow velocity. Hydraulic model experiments were conducted to investigate the armor stability. We found two important factors for armor stability. These were the impingement position of the overflow jet and the harbor-side water level. These effects were taken into account in the method. Numerical analysis on the fluid forces acting on the armor blocks was also conducted to explore the fundamental expression of the new design formula for armor stability. Empirical formulae for the stability estimation were then derived based on the findings from experiments and numerical analysis. The overflow depths of the stability limit corresponding to two failure modes, overturning and sliding, were obtained by two formulae. The stability numbers for each armor unit were determined through the experiments. The estimated results by this method agreed well with the experimental ones. © 2016 © World Scientific Publishing Company and Japan Society of Civil Engineers

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