The Transbay Tube connecting San Francisco and Oakland for BART was constructed the same way. It's much shorter however at 5.8km long vs 18km, but the depth is comparable. Similarly the submerged tunnel section of the Øresund link connecting Copenhagen to Malmö is 4km long.

Discussion (31 points, 47 days ago, 33 comments) https://news.ycombinator.com/item?id=43318793