Abstract
It is conventionally assumed in the analysis and design of earth dams that the soil located above the phreatic line, i.e. the uppermost seepage flow line, is completely dry. However, there is often an unsaturated flow of water through an unsaturated zone above this borderline and variation in moisture content in this zone results in variation of matric suction throughout this region. Variation of matric suction, in turn, results in variation of effective stresses in this zone. In this research, the seismic response of earth dams in terms of the displacement and acceleration at the crown of the dam as well as the stress distribution in the dam body is investigated. Taking into account the effect of unsaturated zone, a comparison is made to investigate the effect of conventional simplification in ignoring the dynamic characteristics of the unsaturated zone above the phreatic line and the more complicated analysis which includes the unsaturated zone. A function for the soil-water retention curve (SWRC) was assigned to the soil in the unsaturated zone to determine the variation of matric suction in this zone and analyses were made using finite difference software (FLAC). Results are then compared to the conventional method for homogeneous dams. In these analyzes the soil shear modulus was assumed to vary with the mean effective stress both for saturated and unsaturated zones. Among various results, it was notable that the history of crest x-displacement, and acceleration show higher values in models accounting for the unsaturated region. It was attributed to the considerably lower values of damping ratio in the crest region in the unsaturated models.
Highlights
For designing earth dams, analyzing the dynamic behavior of the dam against earthquakes is a major step
The multiphase physics of unsaturated region in dams can be very important for such failure mechanisms, there are very few studies on the seismic behavior of dams taking into account the unsaturated region above the phreatic line
Fig 3. depicts the shear modulus profiles of the earth dams with height
Summary
For designing earth dams, analyzing the dynamic behavior of the dam against earthquakes is a major step. In dynamic analysis of the response of unsaturated soils, various studies have employed different assumptions for the effective stress parameter. The importance of considering the difference in saturated and unsaturated soil behavior for designing earth dams has been stated before in the previous studies by Alonso and Pinyol (2008) and Alonso and Cardoso (2010) [8,9]. Mori et al (2011) have modeled the dynamic behavior of a fill slope and have compared it to its monitored behavior and Matsumaru and Uzuoka (2015) have simulated the behavior of the shaking table tests on embankments [10,11] The focus of these studies has, been mainly on the effects of different assumptions for pore air pressure field on the simulation results. The details of the model, the theoretical background of the model and the results have been presented
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