Faculty Profiles - NAKAI, Kentaro

Papers - NAKAI, Kentaro

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Densification/compression by compaction of a granular geomaterial changed by crushing dewatered sludge with air Reviewed

Kentaro NakaiMasaki NakanoKazuhiro Kaneda

The 16th International Conference on Soil Mechanics and Geotechnical Engineering,Osaka, Japan. page： 2307-2310 2005.9

Authorship：Lead author Language：English

To improve the construction surplus soil and to use the soil as a geomaterial, a densification technology of soil with high water con-tent such as dewatered sludge is studied. The densification is brought by the change from the `consolidation material' like clay to the `compactable material' like sand. The soil is crushed with air to an assembly of clay pebbles, the water content of which is ease to de-crease, and therefore the assembly can be compacted to high density without long consolidation time. The soil became low com-pressible and had high shear resistance, which can be describe by Super/subloading Yield Surface model.

Softening behavior with plastic compression on highly structured naturally deposited cla Reviewed

Kentaro NakaiMasaki Nakano

Vol. 8 page： 451-460 2005.8

Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal)

Highly structured naturally deposited clay exhibits the softening with plastic compression due to the decay of soil structure. The softening behavior can be expressed by Super/subloading Yield Surface Cam-clay model, SYS Cam-clay model (Asaoka et al., 2002), in which the concepts of “structure," overconsolidation, anisotropy, and their evolution laws, are introduced into the modified Cam-clay model. In the present study, in order to examine the effects on the softening behavior, the consolidation test with some constant stress ratios controlled by the strain rate was carried out using Joban clay, highly structured clay, and calculated by SYS Cam-clay model. The new findings are as follows. (1) The large compression due to the softening with plastic compression occurs when the stress ratio of consolidation was large, initial degree of structure was large and degradation speed of structure is rapid through the calculation. (2) The experimental results showed the same tendency as the calculation results. (3) The axial strain proceeded by 4% keeping the deviator stress q and mean effective stress p constant axial strain in the consolidation test with stress ratio of 1.3.

Elasto-plactic Description of Undrained Shear Behavior of Sand Depending on Confining Stress Reviewed

Masaki NakanoToshihiro NodaKentaro NakaiAkira Asaoka

International Symposium on Plasticity 2005, Kauai (Hawaii) page： 283-285 2005.1

Densification of dewatered sludge by compaction after crushing and air-mixing mechanical behaviour of structured clay and simulation Reviewed

Nakano, M., Nakai, K. and Kaneda, K.

ASCE Geotechnical Special Publication No.156, Geomechanics II: Testing Modeling and Simulation page： 189-200189-200 2005

*Simulation of shear and one-dimensional compression behavior of naturally deposited clays by Super/subloading Yield Surface Cam-clay model Reviewed

Masaki NakanoKentaro NakaiToshihiro NodaAkira Asaoka

Soils and Foundations Vol. 45 ( 1 ) page： 141-151 2005

Language：English Publishing type：Research paper (scientific journal)

In the present study, undrained triaxial compression tests and oedometer tests were carried out on two types of naturally deposited undisturbed clay, Pleistocene clay and Holocene clay, and the behaviors of these clays were then simulated using the Super/subloading Yield Surface Cam-clay model (Asaoka, Nakano and Noda, 1998, 2000 and Asaoka et al., 2002), in which the concepts of “structure," overconsolidation, anisotropy, and their evolution laws, are introduced into the modified Cam-clay model. The findings of the present study are as follows:
1) For the two types of undisturbed clay, the Super/subloading Yield Surface Cam-clay model can simulate undrained triaxial compression behaviors ranging from the normally consolidated state to the overconsolidated state, corresponding to various isotropic pressures using a single set of material constants.
2) In addition, the model can simulate one-dimensional compression behaviors using the same material constants as those used for the undrained triaxial compression behavior simulation.
3) Both undrained shear and one-dimensional compression behaviors for the two types of undisturbed clay, that is Pleistocene clay and Holocene clay, which have different loading histories and have undergone different ageing effects, were simulated using the Super/subloading Yield Surface Cam-clay model by changing the evolution parameters.

Effect of the slaking susceptibility on one-dimensional compression behavior of crushed Tertiary mudstone assembly Reviewed

Masaki NakanoKentaro Nakai

Vol. 7 page： 685-692 2004.8

Language：Japanese Publishing type：Research paper (scientific journal)

Large amount of Tertiary mudstones appears by the major construction works, and the efficient use of mudstone is expected. But it is well known that Tertiary mudstone exhibits “slaking." In order to use mudstone with advantage, it is necessary to understand the effect of the slaking on mechanical behavior. Tertiary mudstones are used in assembly of crushed mudstone pebbles on using for construction. So, one-dimensional compression tests are carried out for the assembly of two types of Tertiary mudstones having a different resistance to slaking. And then these one-dimensional compression properties are simulated by the SYS Cam-clay model. The findings are as follows. (1) The stress state of the mudstone pebbles with a low resistance to slaking can be existed below the normal consolidation line (NCL) of the remolded mudstone under loading in e-σv space, while the mudstone pebbles with a high resistance to slaking can be existed above the NCL. (2) Through the model, the mudstone assembly with a low resistance to slaking can be regarded as sand, of which structure collapses quickly and overconsolidation loses slowly, while the mudstone assembly with a high resistance to slaking can be regarded as clay, of which structure decays slowly and overconsolidation loses quickly.

Description of “compaction" and “liquefaction" behavior of sand based on evolution of soil skeleton structure Reviewed

Nakai, K, Nakano, M., Noda, T. and Asaoka, A.

Proceedings of 2nd International Workshop on New Frontiers in Computational Geomechanics (IWS-FORTALEZA 2004), page： 29-32 2004

Effect of the initial soil structure on slaking susceptibility of Tertiary mudstone Reviewed

Masaki NakanoKentaro Nakai

Vol. 6 page： 419-426 2003.8

Language：Japanese Publishing type：Research paper (scientific journal)

To examine the effect of the initial soil structure on slaking susceptibility of Tertiary mudstone, one-dimensional compression tests are carried out for three kinds of tertiary mudstone with a different resistance to slaking. These one-dimensional compression properties are simulated by the modified Cam-clay model with Super/subloading yield surface and rotational hardening. The new findings are as follows. (1) The initial stress state of the mudstone with a high resistance to slaking in e-σv space is above the normal consolidation line (NCL) of the clay that was remolded from the mudstone, while the state of the mudstone with a low resistance to slaking is below the NCL. (2) From the model, the mudstone with a high resistance to slaking can be regarded as the high structured and overconsolidated clay, while the mudstone with a low resistance to slaking can be regarded as the heavily overconsolidated and less structured clay.

Elasto-Plastic Description of Shear Behavior after Compaction of Loose Sand Reviewed

Masaki NakanoToshihiro NodaEiji YamadaKazuhiro KanedaKentaro Nakai

Proc. 1st Inter. Workshop on New Frontiers in Comp. Geomechanics (IWS- CALGARY 2002), (Eds A. Yashima et al.,) Calgary, Canada. page： 27-32 2003

Compaction behavior of sand with degradation of structure and overconsolidation Reviewed

Nakano, M., Noda, T., Asaoka A. and Nakai, K.

Proc. of Sino-Japanese Symposium on Geotechnical Engineering, Beijing, China page： 455-462 2003

Elasto-plastic Simulation of Compaction Behavior of Loose Sand due to the Decay of Soil Structure Reviewed

Masaki NakanoAkira AsaokaKazuhiro KanedaKentaro Nakai

Proc. of 12th Asian Regional Conf. on Soil Mechanics and Geotechnical Engineering, Leung et al. Singapore. page： 505-508 2003

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