Comprehensive Instrumentation for Real Time Monitoring of Flux Boundary Conditions in Slope

Rainfall-induced slope failures occur in response to climatic changes in many parts of the world. Climatic changes result in dynamic flux boundary conditions across slope surface, such as infiltration and evaporation. In addition, trees, shrubs and grasses generate another dynamic process of transpiration across slope surface. As a result, stability of a slope as quantified by factor of safety is not constant over time, but varies in accordance with variation in flux boundary conditions. s of flux boundary conditions on slopes can be assessed using real-time monitoring. In this paper, different types of instruments for real time monitoring of flux boundary conditions are illustrated to study the effect of rainfall and evaporation on pore-water pressure and water content in slope. Several geotechnical instruments such as piezometer, tensiometer, time-domain reflectometry and devices for measuring changes in local climate such as rainfall gauge and weather station can be installed within the slope area. The data from these instruments were captured automatically using a data acquisition system and the data were transported to a secured website in real time. Finite element seepage analyses were carried out to investigate the effect of rainwater infiltration and evaporation on pore-water pressure distribution of a residual soil slope at Telok Blangah, Singapore. The numerical analysis results showed a good agreement with those obtained from field measurements if the evaporation was applied in the analyses. This indicated that rainfall and evaporation play important roles in pore-water pressure changes within the residual soil. Seepage analyses were also conducted using different coefficients of saturated permeability and soil-water characteristic curves of the soil. The results showed that good quality laboratory test results are required to closely simulate pore- water pressure distributions within the soil layers.