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Dive into the research topics where Jiro Kuwano is active.

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Featured researches published by Jiro Kuwano.


Geotechnical Testing Journal | 2004

Measurement of Quasi-Elastic Stiffness Parameters of Dense Toyoura Sand in Hollow Cylinder Apparatus and Triaxial Apparatus with Bender Elements

Sushil K. Chaudhary; Jiro Kuwano; Yutaka Hayano

Quasi-elastic stiffness parameters of dense Toyoura sand were measured at various stress states during similar consolidation and p′-constant shear tests in a hollow cylinder apparatus and a triaxial apparatus equipped with local deformation transducers and bender elements. Test results from these two test setups were compared. Although the Youngs moduli from the triaxial apparatus were slightly lower than those from the hollow cylinder apparatus, they followed approximately the same power laws with the effective normal stresses. The shear modulus Gvh from the hollow cylinder apparatus was almost the same as that from the shear wave velocity measurement in the triaxial apparatus. The Poissons ratios were also similar from both test setups. The vertical Youngs modulus was found to be smaller than the horizontal Youngs modulus. The anisotropy in Youngs moduli followed a power law with the effective stress ratio. However, the Poissons ratios were not dependent on the mean effective pressure or the shear stress level. The symmetry of the stiffness matrix was also examined.


Soil Dynamics and Earthquake Engineering | 1999

Modeling of strain dependency of shear modulus and damping of clayey sand

G.X. Wang; Jiro Kuwano

Abstract A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Strain dependencies of shear modulus and damping were simply modeled. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered particularly in the large strain range. The consideration could be made by normalizing G with G′ 0 =AF(e)(σ′ m /σ mr ) n , the initial shear modulus for the effective confining stress of that particular loading cycle, instead of using G0. G/G′ 0 was expressed by a function of γ as G/G′ 0 =1/(1+b g γ) which was almost stress level independent for clayey sands used in this study. The damping ratio was not much affected by the confining stress. The strain dependency of the damping ratio was modeled by h=a h γ/(1+b h γ) . Effects of load irregularity on the shear modulus were also investigated. The excess pore pressure and the residual strain were generated especially when the major peaks in the irregular loading were applied to the specimen. However, G/G′ 0 for the irregular loading could be represented reasonably well by the average curve for the uniform cyclic loading, if the excess pore water pressure and the residual strain were taken into account.


Archive | 2008

Centrifuge Shaking Table Tests on Saturated Reinforced Soil Walls

Jun Izawa; Jiro Kuwano

This paper discusses effects of saturation of backfill on seismic stability of reinforced soil wall by using the centrifuge shaking table tests. Before the shaking table test, static stability of reinforced soil wall with saturated backfill was investigated by raising the water level under the centrifugal gravity. As a result, the wall showed sufficient stability statically. The wall with unsaturated backfill showed higher seismic stability and deformation was not observed in the centrifuge shaking table test. On the other hand, large residual displacement was observed in the case of fully saturated case. The cause of the low seismic stability of the saturated reinforced soil wall was due to the decrease of stiffness of back fill soil following increase of pore water pressure, although no liquefaction occurred. In order to clarify the decrease of stiffness of backfill, relationships between shear stress and shear strain of backfill during earthquake were determined using response acceleration time histories. As a consequence, shear stiffness of backfill wall was about 25% smaller than that of unsaturated one. Additionally, it is considered that the decrease of pullout resistance between soil and reinforcement due to the decrease of effective confining pressure of the reinforcement was also one of reasons too.


Archive | 2007

Effects of Curing Time and Stress on the Shear Strength and Deformation Characteristics of Cement-Mixed Sand

Jiro Kuwano; Tay Wee Boon

This study investigates the coupled effect of curing time and stress on the strength and deformation characteristics of cement-mixed sand over a long period of time, e.g. 180 days, as compared to 7 to 60 days in past studies.


Archive | 2013

Effects of Excess Pore Water Pressure on the Displacement of Failed Dip Slopes in 2004 Niigata-Ken Chuetsu Earthquake

Jianliang Deng; Hiroshi Kameya; Yukika Miyashita; Jiro Kuwano; Reiko Kuwano; L. Z. Chen

The effects of excess pore water pressure on the behavior of earthquake-induced dip slope failure were evaluated by field investigation, laboratory tests and numerical calculation. Two dip slopes which failed in the 2004 Niigata-ken Chuetsu Earthquake were investigated intensively. One is at Yokowatashi, Ojiya, and the other is at Yamakoshi Village (currently Nagaoka City). In both cases, the sliding plane was mainly along a weak thin layer. Laboratory test results showed that excess pore water pressure possibly increased during earthquake and/or during sliding. The displacement calculation was executed by using extended Newmark and Janbu method which considers the effects of irregular geometry of the sliding plane and the excess pore water pressure increase or the strain softening property of the weak layer. The calculation results showed very significant effects of excess pore pressure or strain softening.


GeoShanghai International Conference | 2018

Role of Matric Suction on Shear Strength of Unsaturated Compacted Soil at Low Confining Stress

Ali Murtaza Rasool; Jiro Kuwano

In order to deal with some typical geotechnical problems, such as stability of slopes and bearing capacity of foundations shear strength is considered as a fundamental soil property. The influence of matric suction on shear strength has been recognized and various types of laboratory element tests with suction control or measurement has been performed by many researchers. This study aimed at understanding the role of matric suction on the transformation of shear strength and failure mechanism in unsaturated soil. The method of study was via a series of advanced laboratory element tests of two specific types; (1) constant water content (CW) tests, and (2) fully undrained (FU) tests. The tests were performed using the axis translation technique to measure matric suction. The results indicate that the change in water content has an influence on initial matirc suction. The relationship between matric suction and shear strength is non-leaner, and change in matric suction affects the mechanical behavior of unsaturated soil.


The 8th International Conference on Scour and Erosion | 2016

Investigation into the multiple recent sinkholes in Pokhara, Nepal

Reiko Kuwano; Takashi Kiyota; Rama Mohan Pokhrel; Toshihiko Katagiri; Takaaki Ikeda; Y Yagiura; T Yoshikawa; Jiro Kuwano

Since November 2013, numerous sinkholes have been forming in the Armala area of Pokhara Valley, Central Nepal, posing serious threat to local residents. In order to provide countermeasures for reducing sinkhole risk, detailed investigations into the cause and the formation mechanism of the sinkholes are crucial. Preliminary surveys were conducted in June 2014 and November 2014. Comparison of photos, taken in the two surveys, clearly indicates not only the formation of new sinkholes, but also the re-activation of filled sinkholes. By means of dynamic cone penetration tests and surface wave investigations, qualitative characterization of the soil profile was attained, and shallow weak soil layers which are believed to be the location for future sinkholes could be identified. On the basis of the preliminary field investigation, possible sinkhole formation mechanisms are considered. A risk of sinkhole does not seem to disappear as white turbid water continuously springs. It indicates that the internal erosion of white clayey silt layer is still in progress. In August 2015, a boring was carried out beside one of the largest sinkholes. The overall structure of ground layers was first revealed and a 2.5m high cavity at 7.5-10m deep from the ground surface was found within a thick white clayey silt layer. Further ground investigations including surface wave exploration were conducted in December 2015 and the results are reported.


The 8th International Conference on Scour and Erosion | 2016

Model tests on subsurface cavities below road pavement due to sand eruption from the liquefied ground

Jiro Kuwano; Reiko Kuwano; Y Horiuchi

A significant number of subsurface cavities was found in the liquefied ground after the 2011 Great East Japan earthquake. Using the results of the radar exploration conducted along the coastal area of Tokyo Bay, characteristics of subsurface cavities were investigated. The size and shape of the cavities are larger and thinner compared to those of cavities observed in the non-liquefied ground. A series of model tests was conducted in order to understand the mechanism of sand eruption and underground cavity formation when liquefaction occurs. It was found that the flow rate at the opening seems to be the most important factor for the sand eruption.


Archive | 2013

Theoretical Analysis for Noncoaxiality of Toyoura Sand

Shinya Tachibana; Jiro Kuwano

To predict the mechanical behavior of granular materials, the importance of the noncoaxiality; that is, the noncoincidence of the principal directions of inelastic stretching and those of stress, has been recognized in the geotechnical field. In this study, the deformation characteristics during shearing under the effective mean stress constant and the intermediate principal stress coefficient constant conditions are examined by the elasto-plastic constitutive model in comparison with experimental results on Toyoura sand. In constitutive modeling, the anisotropy in the loading surface and the effect of stress rate tangent to loading surface, both of which cause noncoaxiality, are taken into consideration.


GeoCongress 2012 | 2012

The behaviour of embankment soil with time

M. M. Y. Ali; Jiro Kuwano

Most of the observations in literature so far discussed on time effects had focused on the determination of time-dependent behavior of natural soils, whereas the reported experimental studies of embankment soils are few. Therefore, with an aim to clarify the behaviour of embankment soils with time, sampling of the undisturbed soil was made from about a 40-year old highway embankment. Unconfined compression tests, consolidated undrained (CU) triaxial compression tests with small strain cyclic loading and bender element tests were performed for determining small strain Young’s modulus (E) and shear modulus (G). These mechanical properties were compared with the remolded fresh and undisturbed specimens. Besides undisturbed and remolded fresh specimens, some specimens were also allowed to age in a mold under a constant overburden stress of 50 kPa in a specially designed consolidometer to observe the change in the mechanical properties within relatively short period up to a few weeks. The outcome of the research revealed that the strength and stiffness of embankment soils also increase with time.

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Jun Izawa

University of Tsukuba

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Akihiro Takahashi

Tokyo Institute of Technology

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Jianliang Deng

Shanghai Jiao Tong University

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Yoshiro Ishihama

Tokyo Institute of Technology

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S. M. Shirazi

Universiti Teknologi Malaysia

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