Adjacent Structure Monitoring

Adjacent structure monitoring tracks buildings, walls, and services near excavations for signs of movement.
Excavation removes ground support from neighbouring structures, potentially causing settlement and cracking.
Monitoring methods include precise levelling, crack gauges, tilt sensors, and automated prism systems.
Trigger levels define when movement readings require action such as additional support or work stoppage.
A pre-condition survey records the existing state of adjacent structures before excavation begins.
Vibration monitoring measures the impact of piling, compaction, and heavy plant on nearby buildings.
Settlement typically increases with excavation depth and proximity to the neighbouring structure.
Party wall agreements under the Party Wall etc. Act 1996 may require monitoring as a legal condition.
Monitoring data must be reviewed promptly by a competent engineer who can authorise corrective action.
CDM 2015 requires that risks to adjacent structures from construction work are assessed and managed.

Prevent structural damage	Unmonitored excavations have caused adjacent buildings to crack, settle, and partially collapse, endangering occupants.
Early warning	Monitoring detects the first signs of movement, allowing corrective action before damage becomes irreversible.
Legal obligation	Party wall awards and planning conditions frequently require monitoring as a legal obligation on the contractor.

Do

Don't

Complete a pre-condition survey of all adjacent structures before excavation starts.
Install monitoring points before any ground is disturbed near the structure.
Define trigger levels with the structural engineer before excavation begins.
Review monitoring data promptly after each reading and compare against triggers.
Increase monitoring frequency as the excavation gets deeper or closer.
Stop work and notify the engineer immediately if a trigger level is exceeded.
Monitor for vibration when using piling, compaction, or heavy breaking equipment.
Record all monitoring data with dates, readings, and weather conditions.
Brief the excavation team on trigger levels and who to contact if exceeded.
Continue monitoring until permanent works are complete and readings stabilise.

DON'T start excavating near structures without a pre-condition survey on record.
DON'T delay installing monitoring points until after excavation has begun.
DON'T ignore readings that approach or exceed the defined trigger levels.
DON'T reduce monitoring frequency as excavation deepens without engineer approval.
DON'T continue excavation if the engineer has called a stop on monitoring grounds.
DON'T assume an adjacent building is unaffected because no cracks are visible.
DON'T leave monitoring data unreviewed for days; prompt analysis detects trends.
DON'T rely on visual inspection alone when precise instruments are required.
DON'T remove monitoring points before the engineer confirms readings have stabilised.
DON'T forget to include underground services in the monitoring scope.

See also: Excavation Safety Awareness | Excavation Near Structures

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