What is a settlement plate?
A settlement plate is a measuring device that records how much the original ground sinks after fill has been placed on top of it. It usually consists of a square steel plate with a vertical steel rod or pipe attached. The plate rests on the original ground surface, beneath the fill. By repeatedly levelling the top of the pipe, you can follow how the settlement of the subsoil develops over time. In Dutch it is called a zakbaak.
How does it work?
- Plate on the original surface: the plate moves with the subsoil. Whatever the plate sinks is the settlement of the ground below.
- Extendable pipe: as more fill is placed, the pipe is extended so that it keeps sticking out above the fill.
- Levelling: a surveyor measures the top of the pipe against a fixed benchmark. Subtracting the pipe length gives the level of the plate.
- Time series: regular readings produce a settlement curve, showing whether consolidation is slowing down and when the ground has settled enough.
Application
Settlement plates are mainly used for preloading: extra fill is temporarily placed on soft clay or peat so that the subsoil consolidates in advance. Once the surcharge is removed, the remaining base settles very little. This is common in road building, site preparation for new housing and dike reinforcement. Along a long route, several plates are installed at regular intervals so that differences in settlement become visible.
Practical tips
- Baseline reading: survey the plate immediately after installation and before filling. Without a baseline the readings are useless.
- Protect the pipe: excavators and rollers easily knock plates over. Mark them clearly.
- Stable benchmark: measure against a point that does not settle itself, such as a benchmark on a piled structure.
- Interpretation: have a geotechnical engineer assess the readings and decide when construction can continue.
Related terms
- Absolute settlement
- Differential settlement
- Clay
- Peat
- Load-bearing sand layer
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.