Construction and performance of an instrumented slope under capillary barrier systems

Rainfall-induced landslide is one of the most destructive natural disasters that can jeopardize public safety and lead to costly repair works. This natural disaster occurs frequently in residual soil slopes in many tropical areas. Infiltrating water from rainfall events enter the slope, resulting in a decrease of matric suction due to an increase in pore-water pressure in the slope, which in turns reduce the shear strength of the soil. Capillary Barrier, a fine-grained soil layer (overlying layer) placed over a coarse-grained layer (underlying layer), appears to have high potential to be used in slope to prevent or minimize rainwater infiltration. The difference in particle or pore sizes between the fine-grained layer and the coarse-grained layer causes the distinct difference in their hydraulic properties that produces the barrier effect. As a result, the barrier effect of the capillary barrier system limits the downward movement of water. The infiltrated water is then stored in the fine-grained layer by capillary forces. This infiltrated water is ultimately removed by evaporation and transpiration, lateral drainage through the slope or percolation into the underlying layer and slope. The study concentrated on the construction of a two layer capillary barrier system, one with topsoil and cow grass (common turfing grass that is used locally) and the other without topsoil and cow grass on a slope next to a residential area which had experienced numerous rainfall-induced slope failures. The capillary barrier system was constructed as a slope cover to minimize rain water infiltration to the slope. The slope was fully instrumented with tensiometers and piezometers to investigate the effectiveness of the capillary barrier system. In addition, laboratory works were carried out to determine the basic and hydraulic properties of soils from the site and of the materials used for the fine-grained and coarse-grained layers of the capillary barrier cover system. Furthermore, the study also involved the analyses of the manually monitored readings of pore-water pressures below the capillary barrier system with topsoil and cow grass, pore-water pressures below the capillary barrier system without topsoil and cow grass and in the original slope. The analyses and comparisons of pore-water pressures provided assessments on the performance and effectiveness of capillary barrier system under tropical climatic conditions.Master of Engineering (CEE