Magnetic Extensometer

The system consists of three main parts:

• Access Pipe: A string of flush-coupled PVC pipes installed vertically in the ground. It telescopes to move freely with the soil.
• Magnetic Targets: Ring magnets that slide over the access pipe and are anchored into the soil at specific depths (e.g., every 5 meters).
• Readout Probe: A portable reel with a flat tape and a probe tip containing a reed switch.

We offer two types of magnets to suit installation methods:

• Spider Magnets: Featuring spring-loaded legs (like a spider) that bite into the borehole wall. Used when retrofitting into drilled holes.
• Plate Magnets: Large circular plates that are laid flat on the ground and covered with fill. Used during the construction of new embankments.

To take a reading, the operator lowers the probe down the access pipe. When the probe enters the magnetic field of a target, the reed switch closes, activating a buzzer and light on the reel hub.

The operator then reads the depth from the graduated tape at the top of the pipe. By comparing the current depth of each magnet to its initial baseline depth, the total settlement for each soil layer can be calculated.