STUDY ON MEASURES TO RESTRAIN THERMAL CRACKS AND IMPROVE SURFACE QUALITY OF TUNNEL ENTRANCE CONCRETE LINING

坑口付近覆工コンクリートの温度ひび割れ抑制および表層品質向上対策に関する検討

It is highly possible that the concrete lining at the tunnel entrance will suffer from thermal cracks and drying shrinkage due to its exposure to external air and the scattering of snow melting agent. In this sense, in order to avoid thermal cracks, “localized pipe cooling” and “expansive concrete” were implemented. On the other hand, as an attempt to avoid drying shrinkage cracks and salt-attacks, the “water supply curing system with sheet suction” was implemented on the actual construction site. The effects of these measures on improving quality were quantitatively recorded on site and a three-dimensional FEM thermal stress analysis was modelled. The adoption of these countermeasures reduced the probability of occurrence of thermal cracks by about 30%, the drying shrinkage on the surface was reduced by 50~130×10<sup>-6</sup> and the coefficient of permeability to air was improved by a factor of 1/15~1/4. Further, the effect of expansive concrete utilizing a conventional technology was compared, confirming that implementing the localized pipe cooling method was more effective. 坑口付近の覆工コンクリートは,インバートの拘束による温度ひび割れや乾燥した外気による乾燥収縮ひび割れや積雪地域では融雪剤の飛び散りによる塩害等が発生する可能性が高い.そのため,外部拘束による温度ひび割れ対策として“部分パイプクーリング”および“膨張コンクリート”,乾燥収縮ひび割れや塩害対策として“シート吸引方式給水養生工法”を現場に適用し,これらの品質向上効果を現場計測および三次元FEM温度応力解析により定量的に評価した.これらの対策により,ひび割れ発生確率は30%程度低減,乾燥収縮ひずみは50~130×10<sup>-6</sup>低減,透気係数は1/15~1/4改善する効果が得られた.また従来技術である膨張コンクリートとの外部拘束ひび割れ抑制効果を比較し,部分パイプクーリングのほうが効果が高いことが確認できた.

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  • English
  • Japanese

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  • Accession Number: 01668986
  • Record Type: Publication
  • Source Agency: Japan Science and Technology Agency (JST)
  • Files: TRIS, JSTAGE
  • Created Date: Feb 24 2018 3:02PM