NATMトンネルの二次覆工コンクリート天端部に発生する軸方向ひび割れ抑制のための応力の経時変化の分析

• 資料種別: 博士論文
• タイトル: NATMトンネルの二次覆工コンクリート天端部に発生する軸方向ひび割れ抑制のための応力の経時変化の分析
• 著者・編者: Rankoth, Chamila Kumara
• 著者標目: Rankoth, Chamila Kumara
• 出版年月日等: 2016-09-16
• 出版年（W3CDTF）: 2016-09-16
• 並列タイトル等: Investigation of time dependent stress at crown of second lining concrete of NATM tunnels for mitigating longitudinal cracks
• 授与機関名: 横浜国立大学
• 授与年月日: 2016-09-16
• 授与年月日（W3CDTF）: 2016-09-16
• 報告番号: 甲第1859号
• 学位: 博士(工学)
• 博論授与番号: 甲第1859号
• 本文の言語コード: eng
• NDLC: UT51
• 対象利用者: 一般
• 一般注記: In recent past, tunnel constructions in Japan have increased mainly due to the construction of revival road network in Tohoku region in northern part of Honshu Island. Many of the mountainous tunnels constructed in this area utilize New Austrian Tunneling method which has a superior versatility and low initial cost compared to many of other methods. These tunnels are comprised of a double shell lining system. The Inner lining is constructed with shotcrete and the outer lining, which is visible, is made of reinforced or unreinforced concrete. Cracking of the outer, second, lining has become a major concern for tunnel construction specialists as cracking poses a great threat for long term durability. Three types of cracks were apparent from the tunnel inspection data. The first type of cracks referred to type 1 cracks in this research are the cracks which propagate parallel to the crown line close to the crown region. The second type of cracks type 2 cracks are the vertical cracks starting from the horizontal construction joint between the invert and second lining. The third type of cracks, type 3, are the horizontal cracks starting from vertical construction joint between two lining blocks. It had been observed that the mechanism of type 1 cracking was not properly understood because the stress of crown of the second lining could vary based on many variables such as self-weight, volume changes of concrete, hydration heat, shrinkage, restraint conditions of joints etc. Regarding type 2 cracks, the cause of the cracking was hypothesized as the restraint from invert for volume change of concrete in the second lining. However, further clarification of behaviour of type 2 cracks was required to investigate the potential crack mitigation techniques. Three objectives were set for this study. The first objective was to establish appropriate finite element modeling schemes to study stresses generated in the second lining concrete of NATM tunnels mainly caused by short-term thermal movements due to hydration heat and by long-term drying shrinkage. The second objective was to clarify the mechanism of crown stress behaviour as it was crucial to investigate crack mitigation methods at the crown. The third objective was to propose recommendations to mitigate cracking at critical locations. Critical locations considered here included the crown area with high transverse stress and areas of the second lining close to the invert with higher longitudinal stress. The study was carried out for short-term stress behaviour of second lining governed by thermal stress and for long-term stress behaviour of second lining governed by drying shrinkage. The finite element model of the tunnel was calibrated and sufficiently validated using tunnel field measurement data and proper engineering judgement with observed practical evidence. Validated models were utilized for parametric studies to investigate the stress behaviour at the crown and the bottom of the second lining close to invert. Two finite element modeling tools were utilized considering the different capabilities of software in different aspects. Major finite element package used is known as ASTEA-MACS, which is a well-known software in Japan for thermal stress analysis. This software provides a great flexibility to execute parametric studies. The other software is called LINK3D, that is, an integrated system which is capable of simulating the combined effects of microscopic material behaviour and nonlinear structural behaviour of concrete structures. Because of the integrated multiscale concrete simulation model in the software LINK3D is capable of predicting drying shrinkage with respect to varying environmental conditions, structural geometry and so on. First, finite element modeling was carried out considering the short term stress behaviour of second lining with respect to field measurements. The joint formed by waterproofing sheet and the vertical construction joint in between second lining blocks were modeled with negligible joint strength in shear and in tension where the normal compressive strength was assumed to be non-negligible. The joint between the second lining and invert was modeled with fixed joint conditions. The form removal mechanism was assumed to be equal to the application of gravity load at the time of form removal. Special attention was given in determining the thermal properties of composite waterproofing sheet. The thermal conductivity of the waterproofing sheet was calculated based on previous studies done on geotextiles assuming steady state conditions. It was observed that the established model could simulate the temperature in the second lining and stresses in an acceptable manner. Then to analyze the long-term behaviour of the second lining governed by drying shrinkage, a calculation method was proposed by combining LINK3D and ASTEA-MACS software. The free drying shrinkage strain calculated by LINK3D was used as an input to ASTEA-MACS to carry out the stress analysis. Considering the stress distribution of the stress in the thickness direction at the crown and close to the invert in the calibrated model, it was observed that the crown cracks can be non-penetrating cracks while the cracks close to invert can be penetrating cracks. From the short term simulation results, the mechanism of crown stress variation was clarified. It could be seen that before the form removal the crown stress was governed only by temperature rise and capability of the free movement due to the existence of air void. After the form removal up to a short time, stress behaviour of the crown was governed by self-weight, temperature decrease rate difference in the thickness direction and the deformation behaviour of second lining at the crown. From the parametric study for short term behaviour, it was observed that crown transverse stress was sensitive to prolonged form retention which could cause external restraint. To obtain the advantages of longer form retention, proper care should be taken to make sure that the contraction of the second lining is not inadequately restrained. Among the investigated material properties, the coefficient of thermal expansion and autogenous shrinkage had a considerable influence on the longitudinal stress near invert. It was observed that low temperature concreting might be helpful in reducing the invert longitudinal stress but might not affect the crown transverse stress so much. In the current study expansive additive was observed to be effective in controlling the stresses close to the invert but it might be necessary to be further investigated considering the tensile strength of expansive concrete which was not considered in this study. It could be observed that the tensile stress near the surface at crown was small compared to the tensile strength without considering drying shrinkage. This depicts that the crown cracking might not be generated only by thermal stress and self-weight. Therefore, proper construction and ensured material quality might be the key for preventing early age cracking near the crown. In terms of long-term stresses, drying shrinkage governs the stress at the crown. It was observed that shrinkage property of concrete had a considerable effect on crown stress level and should be taken into account carefully. It could be seen that the crown stress was not highly depended on the tunnel section size. Effect of other factors such as concrete creep, air temperature and humidity variation in the long term should be clarified in future to make an accurate conclusion regarding the belief about increased cracking risk in large blocks with evacuation spaces.
• DOI: 10.18880/0000007695; https://doi.org/10.18880/0000007695
• 国立国会図書館永続的識別子: info:ndljp/pid/10318820; https://dl.ndl.go.jp/pid/10318820
• コレクション（共通）: 障害者向け資料
• コレクション（障害者向け資料：レベル1）: テキストデータ
• コレクション（個別）: 国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文; https://dl.ndl.go.jp/collections/A00014
• 収集根拠: 博士論文（自動収集）
• 受理日（W3CDTF）: 2017-04-02T16:10:31+09:00
• 作成日（W3CDTF）: 2017-02-16
• 記録形式（IMT）: application/pdf
• オンライン閲覧公開範囲: 国立国会図書館内限定公開
• デジタル化資料送信: 図書館・個人送信対象外
• 遠隔複写可否（NDL）: 可
• 掲載誌（URI）: https://doi.org/10.18880/0000007695; http://hdl.handle.net/10131/10563
• 連携機関・データベース: 国立国会図書館 : 国立国会図書館デジタルコレクション; https://dl.ndl.go.jp

• 要約等: In recent past, tunnel constructions in Japan have increased mainly due to the construction of revival road network in Tohoku region in northern part ...

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2023-09-05 再収集

2023-09-05 再収集