Masato Shinji

BACK ANALYSIS FOR TUNNEL ENGINEERING AS A MODERN OBSERVATIONAL METHOD

As complexity and unpredictability exist in nature, careful observations and interpretations of what can be measured in the field become prerequisites for geotechnical engineers to conduct safe and economical construction works. Observational methods have evolved from basic visual procedures, conducted on site, to sets of sophisticated procedures using modernized measuring instruments and computer-based back analysis techniques. From the wide range of procedures available for modern tunneling engineering in this field, the present paper tries to address a series of back analysis procedures in which the identification of strain distribution is sought as the primary goal in order to achieve a solid and reliable routine of observations and data interpretations. The discussion starts by identifying structures and flows of forward and back analyses; and it is then expanded to cover several back analysis procedures, including application examples, formulated for linear and non-linear material behaviors. The current status and limitations of the procedures available are also discussed.

CONSIDERATION ON THE INITIAL VALUES IN TOMOGRAPHIC ANALYSIS METHOD FOR THE SEISMIC REFACTION SURVEY

近年, トンネル弾性波探査にトモグラフィ的解析法 (トモグラフィ法) が用いられる事例が増加したが, 解析に際しては初期速度設定方法が課題となる. 初期速度設定方法として, (1) 解析実績に基づく深度-速度関係を用いる方法, (2) 一様速度を与える方法, に加えて, (3) 簡易ミラージュ層解析結果を用いる方法, (4) 簡易層構造解析結果を用いる方法を提案し, さらに (5) 層構造解析 (はぎとり法解析) 結果を用いる方法, をとりあげ, 切羽強度指数一致率による評価を行った. 検討トンネルにおいては, いずれの設定法も顕著な差は見られなかったが, (3) および (4) が比較的実用的な方法であると考えられた. ここでは, トモグラフィ的解析法における初期速度設定方法とその評価について報告する.

A STUDY ON TUNNELING METHODS FOR TWIN TYPE CLOSED TUNNELS BASED ON THE COMPARISON OF SUPPORT LOAD

従来, 離隔距離1m程度の山岳トンネル工法による都市部の近接トンネルにおいては, 中央導坑を掘削し, 両トンネル間にセンターピラーを構築するめがねトンネルが適用されてきたが, 工期・工事費などで利点の多い無導坑方式めがねトンネルも机上検討の対象となっていた. しかし, 施工実績が無いために, 作用荷重や挙動など未解明な点が多く, 長い間採用されることはなかった. そのような中, 筆者らは下到津トンネルにおいて, めがねトンネルと2種類の無導坑方式めがねトンネルの掘削を試みることができた. これら3種類の施工法はそれぞれ長所・短所もある. 本ノートでは, 支保工の応力計測結果から, 施工法による作用荷重などの違いを比較して, 3種類の施工法の特徴を明らかにし, 工法選定の際の参考資料を提供する.

FULL SCALE TEST AND RATIONAL DESIGN METHOD OF ROCK-LINER WITH CONCRETE

不良な地山におけるTBM掘削時の主要支保部材として開発したTBM用鋼製ライナー (ロックライナー) の適用範囲の拡張を図る目的から, ロックライナーにコンクリートを併用するRCロックライナーの開発を行った. 本報告は, RCロックライナーの設計法の確立を目的に実施した実大載荷試験から得られた知見を示すものである. その結果, 主桁部を鉄筋とみなしてRC断面計算を行ったところ, 理論計算値は実験値によく整合し, 耐力向上・変位量抑制効果が確認された.

AN ESTIMATION ON THE EFFECTIVENESS OF GROUND SUPPORT ON SHORTSPAN ADVANCING DRIFT AS AN AUXILIARY CONSTRUCTION METHOD IN SQUEEZING ROCK

Generally, the bench cut excavation is adopted in squeezing rock. However, advancing drift is used as auxiliary method for the occurrence of large-scale earth pressure in Nikkureyama Tunnel II. This paper studies field measurement data of ,Nikkureyama tunnel II. It examines the effect of bench cut and advancing drift by using 3D-FDM. Also, it proposes optimum drift length and bench length from the above result.

INFLUENCE OF EYE-GLASS-FRAME TUNNEL CONSTRUCTIONS ON GROUND SURFACE SETTLEMENT

Construction of the eye-glass-frame tunnels with a center pillar, which stand very close to each other, tends to increase because of limitation of the land utilization in Japan. Compare to the total number of the tunnels, there are not many constructions of the eye-glass-frame tunnels with a center pillar. In design and construction stage of this tunnel type; it is needed to understand sufficiently the characteristic such as displacement action of the periphery natural ground. This paper used measurement data for statistical analysis to study the influence on ground surface settlement during the construction stages.

A STUDY OF RATIONAL PLANNING FOR SEISMIC PROSPECTING BY USING SEISMIC TOMOGRAPHY

When a seismic survey is performed, it becomes important that seismic rays have passed across the whole tunnel formation. It is desirable for the survey to arrange the shooting and receiving points on the bases of seismic ray traces. However, almost seismic surveys in practice are scarcely examined whether the seismic rays have passed through the depth where the tunnel is designed. In many cases, the reciprocal method such as Hagiwaras method has been used as a seismic interpretation method, however it does not give the way to calculate the seismic ray traces. Therefore, we have adopted the seismic tomography, which has an ability to calculate the seismic ray traces. In this work, we present the way to arrange the shooting and receiving points, which enable the seismic rays to pass across the tunnel formation, by the tomographic simulations. This simulations prior to the survey could bring suitable seismic survey plans.

PROPOSAL OF NEW IDEA FOR TUNNELING METHOD (MULTIPLIED TUNNEL SUPPORT SYSTEM) BASED ON RE-EXCAVATION EFFECT

Tunneling in squeezing ground is often faced with large deformations and high rock pressures. In some cases, re-excavating the rock as well as replacing the tunnel supports is unavoidable for a planned clearance of the tunnel. Instead of such re-excavation method, a new method, the multiplied tunnel support system, is proposed in this report. Moreover, the mechanisms of the two types of methods are discussed on the basis of numerical analyses . It is shown that the multiplied tunnel support system is superior to the re-excavation method in many aspects especially in the bearing capacity of the lining .

A RATIONAL DESIGN OF TUNNEL SUPPORT OF THE 2ND STAGE TUNNEL BASED ON THE 1ST STAGE TUNNEL CONSTRUCTION RECORDS

II期線トンネルの支保設計を行うためには, 双設トンネルとして建設される高速道路トンネルの特徴を生かす設計手法の開発が望まれている. しかし, これまでの事例をみると, I期線の施工データを一部活用し, II期線の設計・施工を実施した事例は数例みられるが, 明確な設計手法として確立されたものはない. 本研究では, 蓄積された多くの双設トンネルの実施工データを比較し, 独自の定量化を試みることで, より合理的なII期線トンネルの支保設計の考え方の検討をした. その結果, II期線トンネルの支保設計は, I期線トンネルの施工支保ランクを基本とするものの, 若干軽めの支保規模を計画し, 情報化施工を実施することにより合理的な施工が考えられることを示した.