Earth Retaining and Stabilising Structures (ERSS) are widely used in Singapore for basement construction, deep excavation, infrastructure works and underground development. During excavation, the retaining system, surrounding ground, groundwater and adjacent structures may all respond to changes in stress and construction sequence.
For this reason, an effective ERSS instrumentation and monitoring programme is not based on a single sensor. It normally combines different instruments so that engineers can assess several aspects of ground and structural behaviour together.
The exact monitoring system must always follow the project design, monitoring specification and requirements of the relevant Qualified Person. The instruments below represent common monitoring functions rather than a universal minimum list.
Singapore’s BCA documentation expressly recognises monitoring of ground lateral movement, ground/building settlement or vertical movement, strut force, groundwater level and pressure in connection with ERSS. For ERSS utility-gap situations, BCA specifically identifies inclinometers, piezometers and water standpipes as a set of geotechnical instruments to be provided in the vicinity of the gap.
1. Inclinometers — Monitoring Lateral Ground Movement
Inclinometers are among the most important instruments for deep excavation monitoring.
An inclinometer casing is installed vertically, normally within the ground or retaining system. Repeated surveys allow the lateral displacement profile to be determined with depth.
Instead of providing only a single movement value, an inclinometer can help engineers understand:
- where movement is occurring;
- how the deformation profile changes with excavation depth;
- whether movement is concentrated at a particular stratum;
- whether displacement is increasing between construction stages.
For ERSS works, inclinometer trends are often reviewed together with excavation sequence, strutting or anchoring activities and adjacent ground response.
Related GEOUE service:https://geoue.com/sg/inclinometer-monitoring/
2. Piezometers — Monitoring Pore-Water Pressure
Deep excavation changes both stress conditions and groundwater behaviour.
A piezometer measures pore-water pressure at a selected elevation. Vibrating wire piezometers are commonly used where engineers require discrete pressure measurements at particular soil layers.
Piezometer data can help identify:
- changes caused by excavation;
- groundwater drawdown;
- response to dewatering;
- pressure recovery;
- unexpected hydraulic behaviour.
The elevation of the piezometer tip is critical because pore-water pressure varies with depth and geological conditions.
Related GEOUE service:/sg/piezometer-monitoring/
3. Water Standpipes — Monitoring Groundwater Level
A water standpipe provides a comparatively simple means of observing groundwater level.
Although a standpipe and a piezometer both relate to groundwater, they do not provide identical information.
A standpipe normally indicates the water level established in the response zone of the installation, while a piezometer can be configured to measure pore-water pressure at a more specific elevation.
Using both instruments can therefore provide complementary information, particularly where groundwater behaviour is important to excavation performance.
4. Settlement Monitoring
Excavation can produce vertical ground movement outside the retaining system.
Settlement monitoring may therefore be installed on:
- surrounding ground;
- roads;
- buildings;
- utilities;
- structural elements;
- other sensitive assets.
Depending on the project, monitoring may use settlement markers, survey points, prisms or other surveying systems.
The engineering value lies primarily in movement relative to an established baseline, rather than the absolute coordinate of an individual survey point.
Related GEOUE service:https://geoue.com/sg/settlement-monitoring/
5. Building and Structural Monitoring
Where excavation takes place close to existing buildings or structures, the monitoring programme may extend beyond ground settlement.
Typical parameters can include:
Crack movement — using crack meters or tell-tales.
Tilt — using tiltmeters or survey methods.
Building settlement — using survey points or prisms.
Structural deformation — where required by the monitoring design.
These measurements help distinguish local structural response from wider ground movement.
Related GEOUE services:https://geoue.com/sg/building-monitoring/https://geoue.com/sg/crack-monitoring/
6. Strut Load and Structural Force Monitoring
A braced ERSS transfers excavation loads through structural components such as walers and struts.
Where specified, load cells or strain-based measurements may be used to assess changes in structural force.
These readings become particularly valuable when interpreted together with:
excavation level → retaining-wall movement → groundwater response → strut force.
No individual parameter tells the complete story.
7. Vibration Monitoring
Piling, demolition, excavation support installation and other construction activities can generate vibration.
Vibration monitoring may therefore be required where nearby buildings, infrastructure or sensitive facilities could be affected.
Typical systems record Peak Particle Velocity (PPV), often in three orthogonal directions, together with the time of the event.
Related GEOUE service:https://geoue.com/sg/vibration-monitoring/
Monitoring Is About Relationships, Not Individual Sensors
A useful ERSS monitoring programme does more than collect readings.
Consider a simplified sequence:
Excavation progresses
→ groundwater changes
→ retaining wall deforms
→ surrounding ground responds
→ strut loads change
→ nearby structures may move.
The value of instrumentation therefore comes from combining different measurements and interpreting them against the construction sequence.
A single unusual inclinometer reading may be a measurement issue. The same displacement accompanied by increasing settlement, groundwater change and structural response deserves substantially greater attention.
From Baseline to Action
A typical monitoring workflow includes:
1. Instrument installation
Install instruments at the locations and elevations defined by the approved monitoring plan.
2. Baseline establishment
Obtain stable readings before the relevant construction activities begin.
3. Construction-stage monitoring
Collect readings according to the required frequency.
4. Data validation
Check unusual readings against instrument condition, historical behaviour and related measurements.
5. Threshold assessment
Compare results with project-specific Check, Alert or Work Suspension criteria where applicable.
6. Engineering review
Interpret trends in the context of excavation and construction activities.
BCA’s ERSS advisory documentation explicitly provides for reporting against Check, Alert and Work Suspension levels when critical monitoring levels are exceeded.
Conclusion
There is no single “standard ERSS instrument package” suitable for every Singapore project.
A robust programme is designed around the failure mechanisms and engineering questions that matter to the particular excavation:
Where is the ground moving?
How much is it moving?
What is happening to groundwater?
How is the retaining system responding?
Are surrounding assets being affected?
The best monitoring system is therefore not the one with the largest number of sensors. It is the one that provides the right measurements at the right locations and turns them into information engineers can act upon.
Suggested internal CTA:
Explore GEOUE ERSS Monitoring in Singapore → https://geoue.com/sg/erss-monitoring/