Technical Studies


Applications of a fiber Bragg grating ground movement sesnor system for slope stability monitoring at Yi-Shing power plant

Yi-Shing power plant is an important hydraulic structure in upstream of the Shin-Men reservoir. A slope failure occurred on March 23, 1986 and caused heavy damage. To assure the safety of the pore plant, a series of monitoring devices have been installed. These sensors included inclinometer casings and tilt-meters. An inclinometer probe (IP) manually lowered into the inclinometer casing is typically used to detect potential ground displacement. The operation and recording of IP readings are usually done by hand. This method is time consuming and dangerous when taking readings in bad weather conditions. Unfortunately, the readings are most valuable under adverse weather conditions. Therefore, automation of slope displacement monitoring systems can be important to enhance the frequency and safety of the feidl monitoring operation. There have been developments of electronic devices capable of performing automated slope stability monitoring. These electronic systems are costly and prone to electromagnetic interferences (EMI) and damage by lightning. Their longevity is compromised when buried underground for a long period of time.

The research team developed an optic Fiber Bragg Grating (FBG) based monitoring system. The sensors are immune to EMI and not affected by humidity when installed underground. The research team drilled a 40 m deep borehole and inserted a series of Fiber Bragg Grating Segmented Deflectometer (FBG-SD) into the borehole as a means to detect ground displacement. The FBG readings were taken manually between June and July. An automated data logging system was added and used from August to October. The feasibility of using the FBG-SD has been verified and the possibility for mass deployment of such systems is evaluated.