Building settlement observation

Building settlement observation is a specialised survey that measures how much, and how evenly, a foundation sinks into the ground over time. Every building settles to some extent and that is normal; what matters is settlement that is too large, accelerating or uneven. Differential settlement is what causes cracks in walls, building tilt and structural damage.

Observation is usually carried out when the design calls for it: tall and critical buildings, weak or collapsible soils, or new construction built directly against an existing one. For older buildings, owners order it when cracks appear, after nearby excavation or water leaks, or before adding storeys, to find out whether settlement is still ongoing.

Steel settlement marks are fixed to walls at foundation or basement level and levelled in closed loops from deep benchmarks placed outside the zone of influence. We run first- and second-order precise levelling with SOUTH digital levels and invar staves, which resolves settlement to fractions of a millimetre.

Each cycle is compared with the previous one, settlement rate and differential settlement are calculated, and graphs are used to forecast when the building will stabilise.

When you need it

• New high-rise buildings where the design requires it
• Construction on weak, collapsible or saturated soils
• When cracks appear in walls of an existing building
• When excavation or construction starts next door
• Before adding storeys or reconstruction

What's included

• Designing the settlement mark layout
• Installing wall marks and deep benchmarks
• Checking benchmark stability
• First- and second-order precise levelling cycles
• Calculating absolute, average and differential settlement
• Determining building tilt

How we work

1. Inspecting the building and recording existing cracks
2. Installing marks and benchmarks
3. Initial levelling cycle
4. Repeat cycles at the agreed frequency
5. Report, graphs and stabilisation forecast

Deliverables

• Layout of marks and benchmarks
• Settlement table for each cycle
• Settlement-time graphs and settlement contour map
• Technical report and conclusion