Application
The Sondex Settlement System is used to monitor settlement and heave in excavations, foundations, dams, and embankments. It can also be installed behind retaining structures, such as sheet piles and slurry walls, and above underground openings, such as tunnels and shafts. The Sondex system indicates the depths at which settlement has occurred as well as the total amount of settlement.
Operation
The Sondex system consists of a probe, signal cable, a cable reel with a built-in voltmeter, and a number of stainless steel sensing rings. A survey tape is typically connected to the probe.
The sensing rings are fixed to a continuous length of corrugated plastic pipe which is installed coaxially with inclinometer casing or access pipe. The annulus between the corrugated pipe and the borehole wall is grouted. The corrugated pipe and its sensing rings settle with the surrounding ground.
To obtain measurements, the operator draws the probe through the access pipe. The buzzer sounds when the probe is near a ring, and the voltmeter reading peaks when the probe is aligned with a ring. The operator refers to the survey tape and records the depth of the ring. A sensitivity adjustment allows operation adjacent to steel pipes, piles, or other metal objects. Settlement and heave are calculated by comparing the current depth of each ring to its initial depth.
Installed Components
Access Pipe: Flush-coupled inclinometer casing is used when inclinometer readings are required. Otherwise flush-coupled PVC pipe can be used. After pipe and magnets are installed, the borehole is backfilled with grout.
Corrugated Pipe: Polyethylene drain pipe with 3 inch or 4 inch ID. Pipe can be installed in a continuous length or in 10 foot sections that are coupled and sealed carefully to prevent entry of grout.
Sensing Rings: Sensing rings are attached to the corrugated pipe at the specified depths. Rings can be attached to the corrugated pipe at the factory or by the user. The bottom ring is considered the datum ring.
