Ground Works
Excavation Monitoring Framework & Contractor Audit
Soil and groundwater monitoring requirements for the excavation safety plan — instruments, baselines, trigger-action-response — and a contractor audit checklist with critical audit-fail conditions.
v2.1Updated 9 Aug 2026ADOSH-SF v4.1 (February 2026)Learning Objectives
- State the mandatory monitoring-plan content required by an excavation safety plan.
- Select instruments and reading frequencies appropriate to the work stage.
- Apply designer-approved Alert / Action / Alarm trigger levels and the response chain.
- Audit a contractor across governance, permits, temporary works, monitoring, dewatering, plant, environment and rescue.
- Recognise critical audit-fail conditions requiring immediate stop-work.
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1. Regulatory Position
CoP 29.0 requires a suitable risk assessment, review of borehole and trial-pit information and water-table conditions, soil survey for larger excavations, appropriate dewatering, competent supervision, and inspections before work, at least daily and before each shift, plus a weekly thorough examination and a further examination after substantial collapse or damage. It does not prescribe a universal instrument list, spacing or numerical limit — the geotechnical and temporary-works designers specify the array, baseline, limits, frequency and response plan.
2. Control Principle
Instruments do not make an excavation safe; they verify that the excavation, shoring and dewatering systems are performing within their approved design assumptions. A missing baseline, failed instrument, unexplained trend or exceeded trigger is a management-of-change event requiring assessment before work continues.
3. Mandatory Monitoring-Plan Content
Design basis and risk model (ground model, borehole/trial-pit data, groundwater regime, adjacent foundations and services, temporary-works and dewatering design, sequence, expected movements and drawdown); instrument schedule and layout with type, reference number, location, depth, installation detail, protected access, owner and drawing reference; baseline and survey datum with pre-construction readings before piling, dewatering and excavation; trigger-action-response plan; frequency and escalation; data assurance and reporting; and integration with the competent-person inspection.
4. Instrumentation Schedule
Typical array: inclinometers in or behind the wall for lateral movement; settlement and heave points inside and outside the excavation; precise-level targets, tilt meters and crack gauges on adjacent structures; piezometers and standpipes inside and outside the cut-off for pore pressure and drawdown; strut load cells or strain gauges; vibration monitors near sensitive receptors; discharge flow and water-quality sampling; and continuous gas and oxygen testing in deep or confined excavations per CoP 29.0 read with CoP 27.0.
5. Frequency and Escalation of Readings
State reading intervals by work stage: baseline, sheet-pile driving, each excavation lift, strut or anchor installation and pre-load, dewatering commissioning, rainfall or flood events, vibration events and abnormal trends. Readings are increased after rainfall, pump failure, vibration event, excavation lift, new strut/anchor stage, support alteration or unexpected ground condition. State when automated continuous data are required.
6. Trigger Levels
Use designer-approved numerical limits in a three-stage system. Green/Normal — reading and rate of change within expected design performance; continue work with routine readings, inspections and trend review. Amber/Action — approaching design tolerance or an unexplained trend; increase frequency, inspect, restrict the causing activity and obtain temporary-works engineer review. Red/Alarm — design limit reached or exceeded; stop work, evacuate the affected zone, implement contingency measures and re-issue the PTW only after engineering assessment and formal release. Generic millimetre limits must not be used without designer approval.
7. Contractor Audit Checklist
Score each line Compliant / Partially Compliant / Non-Compliant / Not Applicable with objective evidence, action owner and due date. A — Governance: excavation safety plan, MSRA, appointment in writing of the Temporary Works Coordinator/Supervisor, excavation supervisor, dewatering supervisor, monitoring lead and Permit Holder; competency records for sheet piling, shoring, dewatering, lifting, temporary electrical work, gas testing and emergency response. B — Permits: correct PTW and linked certificates; validity within one shift or 12 hours with formal revalidation. C/D — Temporary works and utilities: design release, hold points, inspection records, NOCs and service protection. E — Monitoring: baseline, operational instruments, settlement and adjacent-structure targets, pre-condition survey, increased readings after events. F — Dewatering: pump logs recording runtime, flow or totalised volume, pressure/current, well or sump water level, alarms, maintenance and fuel/power status. G — Plant and access: verified working-platform bearing capacity, rigs and outriggers outside edge zones, inspected access and fall-protection systems. H — Atmospheric, environmental and public protection. I — Emergency: rescue method suited to actual depth and geometry, trained rescue and first-aid personnel each shift, radios, emergency access and an unobstructed rescue route.
8. Critical Audit-Fail Conditions
Classify as critical non-conformities requiring immediate stop-work or exclusion of the affected area until rectified and formally released: excavation or support not built to the approved temporary-works design, or unauthorised alteration; no valid PTW or expired/unrevalidated permit; missing utility clearance before intrusive work; dewatering without standby pump or standby power; monitoring absent, unbaselined or failed instruments with no interim control; trigger level exceeded with work continuing; no confined-space controls where the atmosphere requires them; and rescue team, equipment or access not available for the shift.
Knowledge Assessment
1. CoP 29.0 requires excavation inspection:
2. Numerical monitoring trigger levels should come from:
3. Instruments in an excavation:
4. A baseline must be established:
5. At Red / Alarm status the minimum response is:
6. Reading frequency must be increased after:
7. Pump logs should record:
8. Continuous gas and oxygen testing in deep or confined excavations is required by:
9. Which is a critical audit-fail condition?
10. Audit findings should be recorded as:
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