Shinichi Akutagawa

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.

Development of a Fiber-Optic Cable Monitoring System for Storm-Generated Bathymetric Change in the Surf Zone

A monitoring system, called the optic sediment sensor (OSS), for study of the detailed processes of bathymetric changes in the surf zone has been developed. The OSS system consists of an array of fiber gap sensors (FGSs), a support structure (steel pipes), an electronics unit that transmits and receives light through fiber-optic cables, and a data acquisition system. The FGSs are mounted in a 2-m long vertical steel pipe; the sensor spacing is 10 cm. Steel pipes containing FGSs were embedded in the seafloor at two plaices at water depths of 4–5 m beneath a pier at the Hazaki Oceanographical Research Station (HORS) (Port and Airport Research Institute) on the Sudahama Coast, facing the Pacific Ocean, Japan. The electronics unit and the data acquisition system were installed in an observation room on the pier. The OSS systems successfully recorded well-defined and consecutive bathymetric changes caused by storm waves (maximum significant wave-height = 3 m); e.g. reversal of seabed erosion and deposition within a day could be recognized. If the OSS system could be installed in many more locations along the pier, the consecutive process of the formation, migration, and deformation of the whole of the longshore bar may be clarified.

INVESTIGATION ON COLLAPSE MECHANISM OF SUPER-DEEP VERTICAL SHAFT

超大深度地下開発のアプローチとなる超大深度立坑は，その重要性を再認識されつつある．しかし，国内石炭産業の縮小に伴い，深度1,000m級の立坑はほぼ20年以上施工されていない．筆者らは超大深度立坑技術の継承と，定量的な立坑設計技術の確立を目的として，過去に施工された超大深度立坑の技術文献調査，およびかつて施工に従事された技術者からの聞き取り調査を実施し，立坑工事において発生する蓋然性の高い崩壊形態を調査した．その結果，立坑における崩壊のほとんどは高抜けと異常地圧による覆工破損の二つに分類されることが明らかとなった．さらに，その発生状況を検証したところ，この二つの現象は同じ原因により発生するものと判断された．

THE POSSIBILITY OF A NON-DESTRUCTIVE MEASUREMENT OF STRESS TENSOR ON SURFACES OF H-BEAMS USED FOR TUNNEL SUPPORT BY USING A MAGNETIC ANISOTROPY SENSOR

A magnetic anisotropy sensor is used for nondestructive measurement of stress on surfaces of a ferromagnetic material, such as steel. The sensor is built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of a ferromagnetic material. And it can show the absolute values of stresses existing on the surface of the material. Proper treatment of boundary conditions allows determination of stress tensor completely on surface of H-beam flanges, for example. And then we try to use the sensor first to measure stresses on surfaces of four straight H-beams having the length of 2m which is used as structural elements in tunnel support systems.

MEASUREMENT AND IDENTIFICATION OF DEFORMATIONAL BEHAVIOUR OF A TUNNEL RESERVOIR

NATMにより岩盤内トンネル配水池を建設し, 供用前にその一部を利用した湛水試験を実施した. 湛水に伴うトンネルの挙動を詳細に計測・分析した結果, 覆工コンクリートは表面に塗布したコーティング材を通過した水分の浸入により不均一に膨張していることが分かった. 設計時には. 覆工コンクリートには自重と貯留水の水圧だけが作用すると仮定している為, 不均一な膨張挙動により応力・ひずみ分布かどの程度の影響を受けたかを推定するために, 水圧, 温度変化, 吸水膨張, 地山反力を考慮した逆解析手法を開発し適用した. その結果, 不均一な吸水による膨張挙動によって生じるひずみは, 水圧によるそれよりはるかに大きく, 覆工コンクリートの変形挙動に大きく影響を及ぼしていることが判明した.

SELECTION OF OPTIMAL PERIODS OF TIME FOR GPS SURVEYING BASED ON A SKY-PHOTOGRAPH TAKEN WITH A FISH-EYE LENS

GPS (Global Positioning System: 汎地球測位システム) を用いるにあたっては, 観測点近傍の建物や立ち木などによって人工衛星からの電波の受信が妨げられるため, 測定に必要なデータをいかにして確保するかが問題になる. そこで, 本研究では, 測点の上空の障害物の位置を予め写真撮影によって記録する一方, 人工衛星の飛来位置を計算し, これらを照合することにより, それぞれの基線の測量についての経時的な受信可能衛星数を求めるシステムを開発した. このシステムを用いることで, 確実かつ効率的な測量計画をたてることができる.