In-situ monitoring of internal displacements by FBG sensors and slope stability analysis under rainfall infiltration

Abstract

The Wenchuan earthquake in Sichuan Province of China has caused tremendous loss of life and property. The severe earthquake along with the heavy rainfall has induced landslide and debris flows so that the slope stability is a significant concern in this earthquake region. A newly developed inclinometer based on the Fiber Bragg Grating (FBG) sensing technique has been installed in a slope in Sichuan Province for long-term monitoring of internal displacements. A series of FBG sensing bars are installed at different depths of two different boreholes in the slope; meanwhile, all optical fibers of the sensing bars are connected and extended to a monitoring station around 1000m away from the slope site through a main armored cable of optical fibers. Monitoring works are carried out in the monitoring station from 20 June to 25 September 2010. Thus, internal displacements of the slope are analyzed together with the rainfall data which are also collected by a rainfall gauge. The results demonstrate that rainfall infiltration has a strong influence on the internal displacements, while the influence reduces dramatically when the depth exceeds 5.2m. Through a numerical model for the effect analysis of rainfall intensity and duration, the slope stability decreases significantly when the rainfall intensity higher (or equal) than 0.5mm/h and rainfall duration longer than 100h.