Immediately after the launching, a masonry (boulder), wire basket, & tetrapod section of about 20m were excavated, & the remaining 38m was constructed by normal pipe jacking.
At this site, in addition to the excavation of the old revetment masonry (boulder), there was some kind of metal reaction as a result of prior magnetic exploration, so the milling mall method was adopted.
Obstacle masonry groups and tetrapods are very large for TBM with a nominal diameter of φ1000 mm, so it took time to cut.
The jacking pipe also uses a composite steel pipe with a rolling prevention function dedicated to milling moll method.
During the construction, crushed pieces of boulder & wire were excavated, and it was thought that the metal reaction was in this wire basket.