Hydrostatic levelling cell systems precisely measure vertical structural movement be it settlement or heave, in real-time, using a network of connected sensors.

Common uses

Any project that might cause ground settlement via sensitive activities like compensation grouting, excavation, demolition or tunnelling
Structural monitoring of tunnels, tanks, slabs, and embankments
Pile loading tests
Elevators
Track beds and other structures that require precise and stable measurements

Process

This high accuracy system is designed to measure vertical movement and can effectively measure heave or settlement in a 500mm range.

Hydrostatic levelling cells (HLCs) can be installed in basements or around building façades. A 2D network map can then monitor the vertical movement of a structure across the whole footprint. Contour line plots can be generated against time to detect directly which area is to be scrutinised.

All cells are connected by the same liquid tubing and pressurised by a head of water applied by the reservoir to the whole system.

When a cell moves vertically, its corresponding head of water will change accordingly, completely independently of all the other sensors.

As liquid pressure can be measured very accurately at each cell, vertical movement can be calculated based on the density of the liquid used.

Each cell is also linked with an airline to normalise the reference pressure across sensors.

When a structure settles, the cells sinks with it, increasing the pressure. This is then translated into a settlement measurement. Heave is detected in a similar manner when the head of water decreases.

Careful installation ensures that the liquid tubing line is kept free from air, but once established, the most of the system requires no further maintenance.

When water evaporates, the system can be topped up from the reservoir, usually is installed in an accessible location.

Our extensive experience with HLCs (several thousand installed) means it is fully integrated with our software solutions on our web monitoring interface, Quickview. Data is streamed online within minutes from data acquisition, so that construction can be directly guided by the actual ground movement. It can be achieved with simple graphical visualisation, automatic PDF reports, but also automatic alarms raising an email if any set threshold is breached.

This system is especially suitable where conventional survey techniques are not possible.

GEO-Instruments has installed one of the largest systems to date to control settlement and heave in London with 1700 cells.

Advantages

  • High accuracy: The system is extremely accurate, with a resolution of 0.024mm.
  • Integrated data: Structures can be monitored on all sides with one system. It can visually map vertical movement under an entire building with contour lines on a corresponding 2D plan view.
  • Real time data: Data is streamed online within minutes from data acquisition, so that construction can be directly guided by the actual ground movement.
  • Low maintenance: Cells do not need to be accessed and can reliably works for up to five years without intervention.