What causes settlement, why differential settlement is dangerous, and how we measure it.
What is settlement?
Settlement is the vertical lowering of a structure as the subsoil compresses under load or due to groundwater lowering. Uniform settlement is usually harmless; it is differential (uneven) settlement that causes cracks and damage.
Differential settlement
When one part of a building sinks more than another, stresses arise that the structure cannot always absorb. The angular distortion between two points is therefore a key measure of damage risk.
Measuring settlement
Settlement is measured most accurately by precision levelling between fixed bolts, with an accuracy down to 0.2 mm per kilometre. For continuous tracking, hydrostatic levelling systems and automated total stations are also used.