Secant Pile Wall Construction Methodology 

lmao

yup. although i am not sure how the existing floor would be supported aka the new room/basement ceiling, or how the would dig or bore out the earth underneath without it being visible from above

I take the dramamine but it doesn't help

Werner Ziegler

Concrete cap poured over the secant walls will be the new "basement ceiling". Then excavation can begin around the piles. Dirt gets hauled out in the laundry trucks.

The basement slab normally floats independently. Secant piling will not give a watertight structure, only a water resistant one and ground water will seep through giving damp stains. To make the basement watertight a drainage channel is connected to the drainage system and cast in a strip of concrete on the inside of the secant wall and the basement slab is built against the drainage channel slab. Then a wall is built off the basement slab leaving a sealed drained cavity on the inside face of the secant piled wall.