STUDY AND SITE APPLICATION OF PLASTIC GROUT FOR FOUNDATION CONSTRUCTION OF IMMERSED TUNNEL

The Bosporus Crossing Railway Project employed the immersed tunneling method for a part of the 13.5 km length railway crossing the Bosporus strait. Facing to the unprecedented site conditions, plastic grout was used in place of conventional materials like sands and concrete/ mortar in order to construct the immersed tunnel foundation. The plastic grout was infilled in space under the immersed tunnel element after placed on temporary supports at the sea bed. This paper presents the results of studies and site application of the method. Infilling tests were conducted prior to the site application to investigate the infilling behavior and the required infilling pressure of plastic grout. It was demonstrated that infilling from one inlet could cover an entire area of 6m in lateral length and 50cm in height without remaining major voids, and the compressive strengths of the infilling body maintained the design value of 0.13N/mm². Through the experiments, a simple calculation model was also proposed to estimate the infilling pressure. In the site application, about 1,000 m² of the plastic grout was infilled for each tunnel element through the inlets located with 6.6 m spacing on bottom slabs of the tunnel elements. Accuracy of the infilling was examined by checking the fresh properties, monitoring the jack force of the temporary supports and the infilling pressure of the plastic grout. The foundation was successfully constructed without significant trouble nor lifting the immersed tunnel, which demonstrated the effectiveness of the new method. ボスポラス海峡を横断する沈埋トンネル建設においては，海象・地形・地質条件，さらには耐震性に関する要求性能に基づき，沈埋トンネル基礎を形成する函底充填材として可塑性グラウトを用いた工法を初採用した．本論文では，同プロジェクト概要と函底充填に関する技術課題を整理した上で，その適用に向けた事前検討と実施工の結果を詳述する．材料の配合試験に際しては，函底充填に適した配合仕様を設定し，充填性確認実験，実規模実証実験を通してその妥当性を確認した．また，実際の施工に際して，これらの結果に基づき使用設備，施工・品質管理方法を定め，沈埋トンネル全11函の函底充填にあたった．充填材料の1,700mにおよぶ配管圧送を伴いながらも，効率性と確実性を確保しながら施工を完了し，沈埋函基礎としての機能を確保することができた．