"The shield was brought into the chamber first and onto a platform-like restraint system, which allowed it to maintain ring pressure at 40bar so that it could continue installing the cement rings even as it was emerging."

https://www.newcivilengineer.com/latest/how-engineers-at-silvertown-tunnel-are-using-nitrogen-skates-for-a-record-breaking-tbm-rotation-23-03-2023/