#settlement

How a metro tunnel is built — TBM types and why face support decides the machine, the precast concrete ring and its bolts and gaskets, annulus grouting, and the settlement trough that decides what happens to the buildings above.

Why tall buildings and long structures move relative to themselves — settlement under foundations, and elastic, creep and shrinkage shortening of columns and cores — and how level compensation, jacking and delayed connections deal with it.

A storage tank is the most unforgiving foundation problem on a plant: enormous load, applied uniformly, over a circle, with a settlement tolerance measured in millimetres. Here is why the piles are there, why the slab is usually off the ground, and what the hydrotest is really proving.

A tank can go down a long way without complaint, and tilt without much trouble, but it cannot take being bent. The survey exists to separate those three things, because only one of them actually threatens the shell.