Modelling time-lapse shear-wave velocity changes in an unsaturated soil embankment due to water infiltration and drainage
Atsushi Suzaki, Shohei Minato, Ranajit Ghose, Chisato Konishi and Naoki Sakai
Journal name: First Break
Issue: Vol 35, No 8, August 2017 pp. 81 - 90
Info: Article, PDF ( 1.07Mb )
Price: € 30
The partially saturated vadose zone, located between the Earth’s surface and the water table, is made of soil particles, water and air. The water in the vadose zone can be transient percolating water which moves downward to join the phreatic water below the water table or the capillary water held above the water table by surface tension (internal pore pressure less than the atmospheric pressure). The distribution and transport of fluids in the vadose zone have a significant influence on the human life and the environment. For example, the dynamic transportation of fluids in the vadose zone is an important factor which controls the pollution at a near-surface, hazardous waste site (Mercer and Cohen, 1990), affects the desertification in arid/semi-arid areas (Scanlon et al., 2003), and determines the sensitivity of water resources to the climate change (Green et al., 2011). The distribution of water in the vadose zone also affects the microbial processes, e.g., biodegradation, which is necessary in assessing agricultural sustainability (Holden and Fierer, 2005). Last but not the least, the dynamic fluid transportation in the vadose zone causes dynamic changes in the yield strength of the unsaturated soil. Therefore, it is critically important in estimating the stability of earth-retaining structures (e.g., river dykes and embankment dams) and natural slopes (e.g., Collins and Znidarcic, 2004). Soil suction and saturation play an important role in controlling the hydraulic and mechanical properties of unsaturated soil in the vadose zone. Depending on the degree of saturation (Sr), unsaturated soils show different values of suction (s). The s-Sr curve, known as the soil-water characteristics curve (SWCC), is the most important piece of information that characterizes the unsaturated soils. Figure 1 shows a typical plot of SWCC. While the suction is zero at the fully saturated condition, it increases as the degree of saturation decreases. Depending on soil texture, SWCC shows different trends. At the same degree of saturation, clayey soils show larger suction values than sandy soils (Figure 1). This is because clayey soils represent smaller pore sizes (capillary radii) than sandy soils, thus creating a larger capillary pressure (Fredlund et al., 2012).