Why settlement matters
Every embankment settles. What matters is how much, where, and whether the design can tolerate it. On UAE water storage and flood protection embankments, often built on sabkha, uneven settlement can:
- reduce freeboard at the crest
- tear or overstretch the reservoir liner
- open joints in outlet conduits, a classic path for internal erosion
- crack the fill around rigid cut-off walls
First, decide when you need to measure
Most settlement happens while the fill is placed and in the first year after. On a 30 m high embankment, construction settlement can reach hundreds of millimetres, while later settlement is often only tens of millimetres. These need different instruments, so ask the designer for the predicted settlement at each stage before choosing.
The main instrumentation options
Rod extensometers and borehole liquid systems give settlement with depth; plate cells must go in during filling; survey monuments give the absolute crest movement.
Method | How it works | Typical accuracy | Best for |
Liquid settlement, plate cells | Cells laid in the fill read a sealed liquid column to a reservoir on stable ground | ±0.1% of range | New embankments, installed during filling |
Liquid settlement, borehole type | Sensor grouted in rock; reservoir on a plate at the surface | ±0.1% of range (about ±35 mm on 35 m) | Large movements; self-contained in one borehole |
VW borehole rod extensometer | Anchors at several depths, rods to a head at the surface | Better than 0.1 mm | Completed embankments with small movements |
Magnetic extensometer | Magnets on an access pipe, located with a probe | About ±1–2 mm | Large construction settlement; read manually |
Survey monuments or robotic total station | Crest and slope points surveyed against off-site benchmarks | About ±1–3 mm | Absolute and differential settlement |
The liquid in hydrostatic systems is a sealed water–glycol mix. It never carries reservoir water or groundwater.
Getting it right
- Match accuracy to the movement. A 35 m liquid sensor reads to about ±35 mm: fine for construction settlement, too coarse for a 20 mm post-construction trend.
- Anchor the deepest point in rock, or survey the head. Otherwise readings are relative, not absolute.
- Watch differential settlement. Two boreholes far apart will not show it. Add survey points near conduits, cut-off walls and abutments.
- Set trigger levels from the design predictions, for example alert at 80% and alarm above 100–120% of predicted, or when the settlement rate stops falling.
UAE site tips
- Keep loggers and gateways above flood level. Radio does not work underwater.
- Route cables to high ground, never through the liner or cut-off wall.
- A LoRa network with one 4G gateway often beats a GSM modem at every logger.
- Shade enclosures from direct sun and fit surge protection.
How CGT can help
CGT Engineering Consultant and Delma Laboratory review instrumentation specifications, compare instruments and suppliers, supervise installation and interpret monitoring data. Planning an embankment or water storage project? Contact us at info@cgteng.com before the instrumentation is specified.
Frequently Asked Questions
Can instruments be added to a finished embankment?
Yes. Rod extensometers, borehole liquid systems and survey points can be installed from the crest, but only measure settlement from then on.
Can readings be monitored remotely?
Yes. Vibrating wire instruments connect to loggers that send data over 4G or LoRa, with automatic alarms.
How often should settlement be read?
Weekly to fortnightly during construction, monthly in the first year, then quarterly or six-monthly, and after any flood or unusual seepage.