Abstract
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 m3 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.
