Did a job years ago for tank 4m deep sheet piles and hydraulic beams like in Lynch's vid but instead of driving the sheets down we dug around edges first with 18" bucket dropped sheets down back filled set up beams placed one on top of other with top one hooked over top of sheets and lower one chained to one above
Excavated out till top one can't drop anymore pumped it out until solid then dig down till lower one maxed out on chains the pump out to secure it then dig to desired depth of excavation
Did it with my 4.5 hitachi at the time they did get a 7 ton in to dig it but couldn't get the depth my machine had better reach so stayed to do the job only just lifted tank in with it mind

as we filled with concrete we took lower beams out then upper ones then the sheets while concrete was still soft and liquid