Kimitoshi Hayano

Image Analysis Techniques on Evaluation of Particle Size Distribution of Gravel

Particle size distribution of granular materials is usually evaluated by sieve analysis test. In this research, an image analysis technique using ImageJ is proposed to evaluate particle size distribution of gravels. On particular conditions, some differences of gradation curves determined by sieve analysis and image analysis were observed. Based on the results, several aspects related to image analyzing are discussed in the paper. They include appropriate evaluation of particle grain size in image analysis, minimization of shadow effects appeared in images, effects of number of particles adopted for sieve analysis and image analysis and so on. It was found that grain size in image analysis should be defined appropriately to compare the gradation curves by the two methods. Probably, due to light effects, it was also observed that black color sheets are better than white color sheets to place particles. This method can be used as an in-situ test method since this method needs only a camera and a computer.

Shear Banding in a Sedimentary Soft Mudstone Subjected to Plane Strain Compression

A plane strain compression (PSC) testing system to observe shear banding in softrock was developed. The deformation characteristics of shear band in a sedimentary soft mudstone were evaluated by locally measuring axial and lateral deformations of specimens in drained PSC tests. Shear deformation and dilatancy of shear band that occurred between the peak stress state and the start of the residual stress state were on the order of 1 and 0.5 mm. Dilatancy of the shear band continued during the residual stress state, resulting in a high-residual friction angle mobilized along the shear band. Shear band deformation characteristics of two other sedimentary softrocks were obtained from axial strains measured locally in triaxial compression tests based on the stress-state dilatancy relationship obtained from the PSC tests.

Strength Variance within Cement Treated Soils Induced by Newly Developed Pneumatic Flow Mixing Method

In the study, field and laboratory tests were conducted to investigate the degree of strength variance within cement treated soils. The cement treated soils were the dredged soils mixed with a small amount of cement. They were produced by Pneumatic Flow Mixing Method, which had been recently developed in Japan. In the paper at first the outline of Pneumatic Flow Mixing Method system is presented. Then several backgrounds causing the strength variance within the cement treated soils are described. It is found that the cement-water ratio of treated soil s was stable, which was monitored and controlled during their production. The effect of mixing adequacy of the soil-cement mixture and that of non-homogeneity of dredged soils on the strength variance is also discussed. Finally the effective measure to reduce the strength variance is described.

Effects of Sleeper Shape on Lateral Resistance of Railway Ballasted Tracks

In order to reduce buckling problems of railway ballasted tracks, efforts have been made to improve lateral resistance of sleepers. There has been a lot of research on the development of new shapes of sleepers which may increase lateral resistance. However, detailed investigation on the mechanism of improvement has not been studied. Based on the above, a series of model tests was attempted in this study. Six types of sleepers were prepared for model tests. Single-sleeper pullout tests and track panel pullout tests were conducted on the sleepers. The model test results revealed that lateral resistance of the sleepers is significantly affected by their shapes. The idea that the lateral resistance measured at a horizontal displacement of 2.0 mm in full-scale (or 0.4 mm in 1/5-scale) single-sleeper pullout tests corresponds to that in track panel pullout tests is only valid for limited conditions. This is because of the piled group effect in track panel pullout tests, which affects the lateral resistance. Because the degree of the piled group effect is controlled by the ratio of the sleeper width to the sleeper spacing, a significant reduction of lateral resistance may be observed in track panel pullout tests depending on the sleeper type.

True triaxial apparatuses with two rigid boundaries

A small-scale and a large-scale true triaxial apparatuses (where σ1≠σ2≠σ3) were recently developed at the Institute of Industrial Science, University of Tokyo, Japan and are described in this paper. In these apparatuses, a comprehensive loading system that can control both strain rate and stress rate is used for the vertical (axial) direction. In the small-scale true triaxial apparatus, one horizontal load is applied by using a hydraulic system (stress control) while in the large-scale true triaxial apparatus it is applied by using a motor-driven gear system (strain control). Another horizontal load is applied by air or water pressure in both apparatuses. The stresses in three orthogonal directions are controlled independently by a personal computer. Highresolution local measurement transducers are set up in these apparatuses to evaluate normal strains in the three orthogonal directions. These apparatuses have been used in a number of research topics such as anisotropy, time effect, behavior of geo-materials from small to large strains and cyclic loading behavior, among others. It helps to obtain advanced knowledge and understanding of properties of various types of geomaterials including gravelly soils.

Literature survey and experimental study on the direct tension test on rocks

Direct tension tests are indispensable for obtaining an accurate understanding of the deformation and failure characteristics of rocks in tension. For this technical note, the authors collected original papers published in international journals and surveyed the previously reported methods and results of direct tension tests on rocks. Some important factors affecting the strength and stress–strain curve are discussed, such as the shape, size, anisotropy, and water content of the specimen; the loading rate; and the confining pressure. The relationship between the results of the direct tension tests and those of other tests also is discussed. Although various types of testing apparatuses have been adopted in direct tension tests on rocks, the dependence of test results on the apparatuses has not been investigated. In this study, direct tension tests were conducted using various testing apparatuses in seven laboratories. The results of the direct tension tests showed that direct tensile strengths were not dependent on the type of test apparatus used or whether a flexible linkage system was used. The results of the tuff in this study showed that the coefficient of variation of the direct tensile strengths is smaller than that of the Brazilian tensile strengths. Moreover, the results revealed that the coefficient of variation of the direct tensile strengths is comparable to that of the uniaxial compressive strengths of the tuff. The authors noted that to obtain the stress–strain curve from the pre-failure region to the post-failure region, it is necessary to conduct a test with a high-stiffness machine and without a flexible linkage system. This technical note summarized the results of the standardization activity by the authors in the Japanese Geotechnical Society.

LATERAL RESISTANCE CHARACTERISTICS OF BALLASTED TRACKS SUBJECTED TO ANGULAR FOLDING AT STRUCTURE BOUNDARIES

When earthquakes induce local displacements on ballasted tracks at structure boundaries, the lateral resistance decreases and the lateral stability becomes lower. However it is difficult to examine the lateral resistance characteristics under various conditions occurring in the field, so that the knowledge related to this issue have not been accumulated. Therefore, angular folding which is one of the phenomena causing local displacements is focused in this study. After an apparatus which could generate angular folding was newly developed, a series of model tests were conducted. From the model tests, effects of folding angles, the repetition numbers, and the opening or closing status on the lateral resistance were investigated. In addition, differences between lateral resistances from single-sleeper pullout tests and those from track-panel pullout tests were also studied. 鉄道構造物境界におけるバラスト軌道では，地震時に局所的変位が生じると道床横抵抗力が低下し，軌道の水平安定性が損なわれる．しかし，現場で生じる様々な条件下の道床横抵抗力特性を調べることは難しく，いままでに蓄積された資料は乏しい．そこで本研究では局所的変位をもたらすものとして，角折れに着目し，室内で角折れが発生できる装置を製作して模型試験を実施した．模型試験では道床横抵抗力に折れ角の大きさや回数，開閉状態が及ぼす影響，そして1本引き載荷試験と軌きょう引き載荷試験における違いなどについて調べた．

PREDICTION OF LATERAL RESISTANCE OF BALLASTED TRACKS BASED ON LIMITING EQUILIBRIUM METHODS

A limit equilibrium method was focused to evaluate the lateral resistance of ballasted tracks. The method can be easily applied to canted tracks or tracks under seismic condition. In this study, the lateral resistances of ballasted tracks for various shapes of sleepers were estimated based on the method. Lateral resistances under track-panel pull-out loadings were also estimated. The estimated lateral resistances were compared with those obtained from model tests. It was found that the proposed method could well predict the lateral resistance not only for a rectangular parallelepiped-shape sleeper but also for winged-shape sleepers having rectangular or trapezoid sections. It was also found that the lateral resistance under track panel conditions could be reasonably predicted by the method. 鉄道バラスト軌道の道床横抵抗力の推定手法として，複雑な道床形状や地震時慣性力などを比較的考慮しやすい極限つり合い法に着目した．本研究では同手法を用いて，様々なまくらぎ形状，軌きょう水平載荷，という条件下の道床横抵抗力の推定を行った．推定に際しては既往の実験結果と比較することにより推定精度の検証を試みた．その結果，直方体のような単純形状のまくらぎに加えて，台形断面や翼付き形状のまくらぎの道床横抵抗力の推定が可能であることが明らかになった．さらに一本水平載荷だけではなく複数のまくらぎを同時に水平載荷する，軌きょう水平載荷条件下の道床横抵抗力の推定にも同手法が適用できると考えられた．

Centrifuge model tests on dynamic behavior of quay wall backfilled with granulated cement-treated soil

In order to maintain the depth of waterways and sea basins, huge amounts of soft clayey soil are dredged at many ports every year in Japan. In recent years, it has become more difficult to secure disposal areas for dredged soil due to environmental and economic restrictions. The effective use of the dredged soils is therefore required. Granular treated soil, which is dredged clay mixed with cement and polymer, has been developed as a countermeasure against this background and expected to be practically used for reclamation, backfill or subsoil materials. In this study, a series of dynamic centrifuge tests on applicability of granular treated soil to quay-wall backfill was conducted. The test results indicated that backfill of granular treated soil can reduce lateral displacement of caisson and that such backfill is resistant to liquefaction because of its high permeability.

Physical and mechanical properties of cement-treated granular soils with respect to geotechnical application

To utilize soft clayey soils as construction materials, granulating technique is introduced. The technique converts soils dredged at ports and harbors to granular materials by adding small amounts of cement and polymer. Particle density, particle shape and particle distribution characteristics of cement-treated granulate soil (CTGS) as well as stress–strain relationships were investigated from laboratory tests. The results showed that CTGS was a lightweight material because small voids may be included in the particles. In addition, it was found that CTGS showed ductile behavior with the volume contraction when CTGS was subjected to shear deformation even if CTGS was initially prepared by compaction.