I think this sentence says a lot:
'It was painstakingly slow and unpleasant work due to terrible air quality and ingression of filthy Thames water'.
There is a fine animation (Brunel Museum page)
cover tunnel photo by: Matt Brown from London, England / CC BY
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https://www.thebrunelmuseum.com/digging-the-tunnel/
Digging the Tunnel
www.thebrunelmuseum.comThirty-six miners stood in individual cells inside the Tunnelling Shield. They faced a wall of wooden planks held in place by iron rods and butted up against the soil. Each miner would remove one plank at a time and dig away the soil to a depth of...