Katsumi Muramoto

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．

COUNTERMEASURE OF ROADBED DEFORMATION UNDER TRAIN LOADS BY DEEP MIXING METHOD

The roadbed vibration under train loads is affected by the subgrade stiffness, the roadbed vertical displacement increases with a decrease of subgrade stiffness. Thereby, the burden on track maintenance work also increases. The deep mixing method is one of countermeasures which reduce the roadbed displacement under train loads in order to lighten the burden on track maintenance work. This present paper describes the outline of the simulation of roadbed displacement under train loads and the prediction of improvement effect by the deep mixing method using FE (finite element) analysis. 列車走行時の路盤の変位は鉄道軌道を支持する路床・路盤の剛性に依存し，列車走行時の路盤の変位が大きくなると軌道の保守量が増加する．そこで，本研究では，剛性の低い盛土区間を対象として，列車走行時における路盤の変位低減対策として行う深層攪拌混合工法の効果の予測と確認を行った．その結果，2次元FEM解析であっても，物性値や載荷荷重，攪拌混合杭と地盤との複合地盤を適切にモデル化することにより，実測値をシミュレートでき，改良効果をある程度予測できることがわかった．

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．

Repair Method for Ballasted Track by Composite Filling Material Consisting of Water Glass and Polymer

When ballasted tracks include a high-mix ratio of fine particles, track irregularities tend to increase soon after track maintenance performed by tamping because the density change of the ballast is large, and such work impairs the density of the ballast. Therefore, in this study, a method is developed to fill gaps under sleepers with a filling material for the realignment of tracks without impairing the density of the existing ballast. The authors also performed testing to confirm the validity of the method. The results confirmed that this technique is an effective approach for the repair of ballasted tracks.