Development of Monitoring, Non-destructive Testing, and Diagnosis Techniques for Dam Safety (3/3)
Taiwan is located in an area that is prone to earthquakes and typhoons. Recently, there are additional concerns of unusual weather conditions. The safety of reservoirs relies on scheduled and unscheduled evaluations and analyses. Field testing and monitoring are important aspects of these safety measures. Malfunctions of monitoring system and lack of systematic feedback analysis from monitoring data are common problems for dam safety management in Taiwan. Even without breakdowns, the points of instrumentation represent extremely small portions of the areas involved. There is a great demand to enhance our capabilities to monitor and evaluate the integrity of reservoirs. The objectives of this study are to develop improved monitoring techniques and establish a more effective dam safety diagnosis system. Fiber Bragg Grating (FBG) and Time Domain Reflectometry (TDR) sensors transmit their signals via light and electromagnetic pulses, respectively. These sensing techniques are passive in nature, with their electronic interrogation systems placed on the ground surface. The FBG and TDR sensors are durable and capable of distributive installation, very suitable for long term reservoir safety monitoring purposes. The main tasks for this research work include the continued improvement of the previously developed FBG and TDR sensors, and field applications of FBG and TDR sensors at the Shin Shan reservoir. For the FBG sensors, the research team modified the mechanical design and doubled the resolution of the FBG piezometer. Two of the electronic piezometers originally installed on the down-stream slope of the Shin Shan earth dam were replaced with the FBG piezometers. An array of FBG inclinometers along with an FBG piezometer were inserted in an existing inclinometer casing situated in the right bank of the Shin Shan reservoir. All FBG sensors have been connected with fiber optic cables to a centralized interrogation/transmission system for long term automated and on-line monitoring. For the TDR sensors, large scale model shear box tests were carried out to simulate the ground and TDR conditions in Shin Shan reservoir. A TDR ground shearing monitoring system has been installed in the right bank of the Shin Shan reservoir. A Standard Operation Procedure has been prepared for the installation and data analysis of TDR sensors. A manual on non-destructive testing has been prepared to cover the applications of seismic refraction, surface wave, resistivity imaging, and natural electro -potential and ground probing radar methods. The manual guides the user through the selection of non-destructive testing methods in a two-tier, three step procedure. As for the dam safety diagnosis research, the main objective was to establish a system identification scheme for earth dams. The seismic records taken from Li Yu Tan and Mu Dan earth dams were analyzed using time domain, spectral analysis and system identification techniques. The applicability of these techniques for the safety evaluation of earth dams was reviewed. Numerical schemes based on MATLAB and EXCEL for simplified spectral analysis developed for reservoir operators have been developed. A simplified system identification scheme for immediate safety evaluation of the earth dam based on post earthquake seismic records has been proposed.