SLOPE INDICATOR - SETTLEMENT CELLS

Application

Settlement cells are used to monitor settlement and heave in soils. Typical applications include:

• Monitoring settlement or heave in embankments and embankment foundations.

• Monitoring subsidence due to tunneling and mining.

• Monitoring consolidation under storage tanks.

• Monitoring settlement due to dewatering or preloading.

• Monitoring settlement in fills.

Operation

A settlement cell consists of a liquid reservoir, liquid-filled tubing, and the settlement cell, which contains a pressure transducer. One end of the tubing is connected to the settlement cell, which is embedded in fill or installed in a borehole. The other end of the tubing is connected to the reservoir, which is located away from the construction area.

The transducer measures the pressure created by the column of liquid in the tubing. As the transducer settles with the surrounding ground, the height of the column is increased and the settlement cell measures higher pressure. Settlement is calculated by converting the change in pressure to millimeters or inches of liquid head.

Advantages

• The reservoir and readout station can be located away from the construction area. The cell and tubing are buried and do not interfere with construction activities.

• Vibrating wire cells can be automated. The vented version is the most precise settlement cell and automatically compensates for changes in barometric pressure. Tubing lengths of up to 300 m (1000 feet) are permissible with VW cells.

• Pneumatic cells are less expensive and a good choice in lightning-prone regions.

Limitation

• Temperature changes in reservoirs and above ground tubing can affect the repeatability of readings.
• Non-vented VW cells require corrections for barometric pressure (vented VW cells do not).
• Pneumatic cells take longer to read and generally should not be used with tubing lengths longer than 100 m (300 feet).