Application
- The multipoint liquid level system from Interfels is used to monitor small changes in the elevation of settlement gauges that are distributed around a structure. Typical applications include:
- Monitoring differential settlements in structures affected by nearby excavation, tunneling, and unexpected ground conditions.
- Controlling compensation grouting.
Operation
Components of the system include a number of settlement gauges, an automatic level controller, and interconnecting tubing. One gauge is designated to be the reference gauge and is installed at a stable location outside the area affected by settlement. The other gauges are fixed to the structure at selected locations.
Each gauge is connected by tubing to the automatic level controller, which is installed at a central location so that tubing lengths are minimized. Liquid is pumped into the tubing and gauges until the liquid within each gauge rises to the same elevation as the liquid in the level controller. The level controller then holds the elevation of the liquid constant by means of a pump, reservoir, and overflow unit.
Sensors monitor the height of the liquid within each gauge. When settlement or heave occurs, the sensor detects an apparent change in the height of the liquid. In fact, the gauge and sensor have moved relative to the elevation of the liquid surface, which has remained constant. The system is typically connected to a data logger that provides continuous monitoring and stores readings in memory.
Data processing involves computing movements by comparing the current reading from each sensor to the reading obtained from the reference gauge and applying corrections for temperature and, if necessary, for movement of the reference gauge.
Advantages
Accurate Readings: The LVDT sensor in each gauge provides a resolution of 0.01 mm. System accuracy is plus/minus 0.3 mm after corrections are applied.
Settlement Profiles: The settlement system provides multiple independent settlement measurements which can be used to compute settlement profiles.
Automatic Data Collection: The settlement system can be connected to a data acquisition system for full-time, unattended monitoring. The logger stores both level and temperature readings and can transfer data to a computer for near-real time updates of graphs and tables.
