Wire Extensometer Based on Optical Encoder for Translational Landslide Measurement

Abstract

A landslide is a natural disaster mostly accompanied by heavy rains, earthquakes, or volcanic eruptions. Due to its significant incurred losses, several studies have been conducted to develop a landslide monitoring system. In this report, we built and implemented optical-based wire-extensometers to measure and monitor a translational landslide in a prone area. This extensometer was built of an optical rotary encoder (whose shaft bonded to a spiral spring and sling rope) interfaced to a low-cost microcontroller as a principal component and subsequently linked to a GSM-based wireless network. The working principle of the employed sensor described in this paperwork is to count optical pulse signal and convert it into a length unit. This sensor can provide much better signal stability and show high resolution for a wide-range measurement than voltage- or current-based sensors. The specification of the engaged optical encoder provides 2000 pulses per rotation, leading to a length resolution of 0.011 ± 0.0083 mm with a speed limit of about 36 mm/s. Furthermore, the wire extensometer was examined in a remote place near a double-track train road to assess its performance in an actual field. A solar cell system was applied as its main power supply. An example of transmitted data shows a land shift from 12 mm to 150 mm, which is mainly triggered by high rainwater infiltration. This result demonstrates that the developed extensometer is deserved to be promoted for landslide monitoring in the geological research-work area.