Stability monitoring of rainfall-induced deep landslides through pore pressure profile measurements

It has long been recognized that field hydrological and geomechanical properties/conditions are the key elements controlling the stability of a slope under the influence of rainfall. Warning systems based on rainfall or ground displacement measurements are popular methods currently being used to minimize the hazards of landslides. When field hydrological monitoring is used, it usually involves a limited number of sensors for either positive or negative pore-water pressure measurements. The available numerical schemes that couple pore-water pressure with a geomechanical analysis are the most suitable for shallow slope failures. Due to the variable and transient nature of the hydrological conditions in earth slopes, field measurements that reflect the pore-water pressure profile on a real-time basis would be highly desirable. Thus, the authors have developed a piezometer system that is based on optical fiber Bragg grating (FBG) pressure sensors. With this system, an array of nine sensors was installed in a single, 60-m-deep borehole to monitor the pore-water pressure profile in a highway slope in Southern Taiwan. This paper describes the details of the FBG sensor array installation in the field and the data obtained throughout three typhoons from 2008 to 2010. The results demonstrate that the field readings can be readily incorporated into the existing mechanics-based analytical framework and can predict the potential of an upcoming slope failure.