During the construction of the lower stage (φ1350mm slurry type pipe jacking method, construction by another contractor), there was a hard soil obstacle & the bit was damaged, so the design was changed. In order to safely launch & reach, the press-in caisson wall (which was supposed to be unreinforced but actually contains a little rebar) was cut at L = 0.9m on the launching side & L = 0.3m on the reaching side.