22/05/2026
Did you know the walls you walk past every time you go underground cost millions — and were built before anyone even dug the space? 🚇
That massive steel structure being lifted by a crane? That’s a diaphragm wall rebar cage — and it’s about to disappear underground forever.
Here’s how it works:
🔩 A deep trench is dug into the earth — sometimes 30 to 40 metres down
🦺 This rebar cage is lowered in, then concrete is pumped around it
🧱 What forms is a reinforced underground wall — before any excavation even begins
That wall becomes the structure that lets engineers safely hollow out the earth inside it. It holds back surrounding soil and groundwater. It protects every road, building, and utility line above and beside it.
And eventually? It becomes the very walls of the underground spaces you move through every day — the platform, the concourse, the passageways, the walkways connecting one exit to the next.
Next time you’re underground, look at the walls around you. Built deep into the earth. Buried before the space even existed.
You’ve walked past them your whole life and never knew it.
💾 Save this — construction is more fascinating than most people realise.
