I like that, with a grout curtain being impractical and steel being steel with its affinity for oxidation and corrosion in salt environments.
Can you backfill under pressure, as a slurry that sets up later, or do you have to keep the trench unwatered until you've backfilled it?
In order to keep a trench like that open, it is filled with a bentonite slurry that has a higher density than water. That keeps hydrostatic pressure working outward on the trench walls.
When the backfill material is placed, it is dumped at the top of the trench and it slides down a ramp of unexcavated material or previously placed backfill in such a way that it does not drop through the liquid slurry and separate as it reaches the bottom.
Glancing through Google, this reference seems like a fairly decent one. If this doesn't answer all your questions, let me know.
http://www.tceq.state.tx.us/comm_exec/forms_pubs/pubs/rg/rg-282_189585.pdf
Sometimes in lieu of a slurry trench, a jet-grout wall or soil mix wall is used. Those consist of overlapping vertical cylinders, and on deep holes, if the alignment isn't perfect (With in one half of a percent) the wall/curtain is flawed and will not perform as necessary. The slurry trench is guaranteed by the nature of excavation to provide 100% coverage, and long as the backfilling method is done correctly
Big Dig (in Boston) used that parts of that technology: But not everywhere. Expensive.