SLOPE INDICATOR - EL SLED SENSORS

Application

The EL sled sensor is an economical tilt sensor for in-place inclinometer applications, such as:

• Monitoring deformation of diaphragm walls supporting deep excavations.
• Monitoring deformations of embankments and retaining walls.
• Monitoring landslide areas above dams, highways, and railroads to provide early warning of slope failure.
• Monitoring stabilization measures such as compensation grouting (horizontal version).

An in-place inclinometer system consists of inclinometer casing and a string of tilt sensors, such as the EL sled sensor. The inclinometer casing is installed in a vertical borehole that passes through a suspected zone of movement. The sensors, each connected to the next at a pivot point, are positioned inside the casing to span the zone of movement. When ground movement occurs, the casing is displaced, causing a change in the tilt of the sensors inside.

The sensors measure tilt, the angle of inclination from vertical. The tilt measurement is converted to lateral deviation using the formula L sine theta, where L is the gauge length of the sensor and theta is the angle of tilt. Displacement, the lateral distance the casing has moved, is calculated by finding the difference between the current and initial deviations.

In most applications, sensors are connected to a data acquisition system that continuously monitors movements and can trigger an alarm when it detects a change, or a rate of change, that exceeds a preset value.

Rigid Gauge Tubing: Reliable detection of movement and related displacement calculations require straight-line sensor gauge lengths. Rigid gauge tubing satisfies this requirement.

EL sled sensors differ from EL in-place inclinometer sensors in several ways:

• EL sled sensors are intended for one-time installation. IPI sensors have wheels that allow easy retrieval and reuse.

• EL sled sensors are uniaxial and measure tilt in one plane only. EL IPI sensors can be supplied in either uniaxial and biaxial versions.

• EL sled sensors are typically supplied with less sensitive electrolytic vials. EL IPI sensors are supplied with higher performance, but higher cost electrolytic vials.

• IPI sensors can be supplied with built-in multiplexing, which simplifies installation and wiring when many sensors must be used in one inclinometer casing.