Yoshitsugu Momoya

Design and construction of pavements and rail tracks : geotechnical aspects and processed materials

Design and Construction of Pavements and Rail Tracks - Geotechnical Aspects and Processed Materials is a compilation of selected contributions produced between 2002 and 2005 by the International Committee TC3 - Geotechnics of Pavements of the International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE), a committee dedicated to gathering current knowledge of geotechnical aspects relating to pavements and rail tracks. The volume presents advanced procedures for laboratory and field materials characterization, including processed materials (non-conventional road construction materials), novel tests for field stiffness evaluation, a pre-standard for roller integrated continuous compaction control and new theories for evaluation of the long term performance of materials, including environmental aspects. These contributions represent the latest developments relating to the design, construction and long term performance of pavements, rail tracks and earth structures, with emphasis on the geotechnical and environmental background.

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．

A STUDY ON APPLICATION OF PREPACKED CONCRETE TRACKBED FOR SHINKANSEN

The authors carried out laboratory experiments to confirm a compressive strength, a bending strength and a bending fatigue strength of a prepacked concrete which was made by injecting mortar into crushed stones replacing ballasts. Then, they performed a full-scale model cyclic loading test to investigate a strength and subsidence inhibitory effect of the prepacked concrete trackbed. By the full scale test, it was confirmed that the prepacked trackbed has sufficient strength to support the train load after two hours of the injection. Finally, the authors confirmed the performance of the prepacked concrete trackbed based on a design standard of track structure. 既存のバラストから置き換えた砕石に急硬性モルタルを注入することで形成するプレパックドコンクリートの圧縮，曲げおよび曲げ疲労強度を実験により確認し，圧縮強度との関係を示した．また，実物大軌道模型を用いた載荷試験により，プレパックドコンクリートを道床に用いた軌道の耐力および沈下抑制効果を確認するとともに，若材齢時において初列車を通過させることが可能であることを確認した．さらに，有限要素解析により算出したプレパックドコンクリートの応力と各種強度を用いた性能照査により，新幹線用のアスファルト路盤上におけるプレパックドコンクリート道床の適用について，安全性と使用性を評価した．

A STUDY ON RAILWAY ROADBED IMPROVEMENT METHOD TO REUSE DETERIORATED BALLAST OF EXISTING LINE ON SOFT ROADBED

Regarding ballasted tracks on soil roadbeds, it is necessary to perform the roadbed improvement at locations where the ballast includes a high mix ratio of fine-particles and the bearing capacities of roadbeds are insufficient. In the roadbed improvement of such locations, the deteriorated ballast is discarded as surplus soils in most cases. Then, the authors have developed a new method able to be executed simply and in short working time to reuse the deteriorated ballast mixed with grout. In this study, they confirmed a settlement reduction effect of the method by full-scale model tests for soft clay roadbed. In addition, the authors performed also the field test on an existing line laid on soft roadbed to validate a roadbed improvement effect of this method. 土路盤上のバラスト軌道において，道床・路盤が不健全な箇所は道床交換すると共に路盤改良を行うことで健全な状態を保持することができる．一方で，そのような箇所の路盤改良ではバラストが発生土として廃棄されることが多い．そこで，筆者らは発生バラストに低強度グラウトを充填する新しい路盤改良工法の開発を行っている．本工法は，道床交換の際に発生する道床バラストを活用することで環境負荷の軽減とともに作業時間の短縮を目指したものである．本研究では，要素試験により発生バラストを用いた改良体の強度特性を把握した．また，路盤剛性の低い粘性土路盤の実物大模型試験を行い，本路盤改良工法の沈下抑制効果を確認した．さらに，路盤剛性の低い鉄道営業線において試験施工を行い，本工法の路盤改良効果を検証した．

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．

A STUDY ON RAILWAY ROADBED IMPROVEMENT METHOD BY REUSING DETERIORATED BALLAST

At locations where the bearing capacities of roadbeds are insufficient, settlement of ballasted tracks become large, and they should be repaired at short maintenance intervals. At such locations, the improvement method to replace weak roadbed material with strong material such as cement treated soil is occasionally applied. However, since it is necessary to make sufficient compaction of those materials by vibration rammer, it is difficult to execute sufficient extension of improvement length, restricted by the short working-time during the night when trains are not in operation. Therefore, in this study, the authors have developed a method to improve sufficient length of roadbed with short time by reusing the ballast mixed with grout. In this research, they evaluated the effectiveness of this method by elemental tests, realscale tests and FEM (finite element method) analysis. バラスト軌道において，路盤状態が特に悪い箇所では軌道補修を頻繁に行う必要がある．そのよう箇所では，不良な路盤土をセメント安定処理土などの強度の高い材料に置き換える路盤改良が有効であるが，路盤材を振動ランマ等で十分に締固める必要があるため，夜間の短時間では十分な施工延長を確保することが困難であり，発生土の処分も必要となる．そこで，本研究は，路盤改良に伴って発生するバラストを再利用し，急硬性のグラウト材と混合することにより短時間で施工が行えるとともに環境負荷を軽減することができる路盤改良工法を新たに開発するため，要素試験，実物大載荷試験およびFEM解析を行い路盤改良の効果を定量的に評価した．

Performance Evaluation of Reinforced Concrete Roadbed for Slab Track on Clay Subgrade

A high bearing capacity for subgrade is essential to avoid excessive settlement in constructing slab tracks on earth structures. However, a soft diluvial clay layer was detected on part of a Tohoku-Shinkansen line under planning adjacent to the local town of Shichinohe. To address the problem, a double-line-integrated reinforced concrete roadbed was developed. We carried out detailed ground investigations to evaluate the performance of the concrete roadbed on the soft diluvial clay on which the slab track is to be constructed. We further carried out on-site cyclic loading tests involving the application of a vibration machine. Based on the results of these investigations and tests, we carried out FEM analysis to evaluate the deformation characteristics of the concrete roadbed. The results of the FEM analysis clarified that the double-line-integrated reinforced concrete roadbed was able to appropriately support slab track on the soft diluvial clay subgrade.

A STUDY ON DEFORMATION CHARACTERISTICS OF FREIGHT CONTAINER YARD PAVEMENT BY SCALE MODEL TEST

In recent years, large forklifts with heavy wheel load are increasingly introduced to the freight container yard. In the current design of freight container yard pavement, theoretical design method based on multi-layered elastic analysis is applied. However in the case of freight container yard, wheel loads of forklifts are significantly larger than the traffic loads on the roads. To investigate the deformation characteristics of asphalt pavement under heavy wheel load, moving wheel loading tests were carried out On the other hand, ground contact area of forklift tires change with carrying containers. Because the tread of forklift tire is greater than the thickness of pavement, strain in the pavement is significantly influenced by ground contact area. In this study, FEM was introduced to estimate the effect of ground contact area on the strain in the asphalt pavement