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Researcher, Civil Engineering Department, University of Basrah, Basrah, Iraq
Professor, Department of Civil Engineering, University of Basrah, Basrah, Iraq
The application of sand as shell materials in zoned earth dams is common due to its availability and economic factors. Nevertheless, it is necessary to analyze the performance of such materials under the simultaneous effect of seepage and earthquake loads, especially when the core of the structure is formed from low permeable materials. The present work evaluates the influence of polypropylene fiber and cement additions on the seismic performance of sand-shell zoned earth dams. Three small-scale physical models with equal geometry and silty clay cores were prepared and tested using a shaking table in a laboratory. The physical models involved an unreinforced Sand–Silty clay dam, polypropylene fiber-reinforced sand-shell dam containing 0.5% fibers based on dry weight, and a cement-strengthened sand-shell dam with 3% cement content. The steady state seepage analysis was carried out at first; subsequently, the seismic test with the El Centro earthquake was carried out with the PGA values of 0.1, 0.2, 0.3, 0.4, and 0.5 g. The seepage discharge was relatively constant at values between 2.41×10⁻⁷ and 2.75×10⁻⁷ m³/s/m, confirming the dominant control of the silty clay core on the seepage process. For the applied earthquake load, the acceleration magnification, deformation, increase of pore-water pressure, and damages were highest in the untreated model. Under the acceleration of 0.5 g, the settlement on the dam's crest was 26 mm, 18 mm, and 5 mm in the untreated model, the fiber-reinforced model, and the cement-treated model, corresponding to reductions by 31% and 81%, respectively. In addition, the maximum width of cracks decreased from approximately 125 mm in the untreated model to 15 mm and 5 mm in the fiber-reinforced model and the cement-treated model, respectively. The effectiveness of stresses and factors of safety was higher for the cement-treated model than other models through the entire loading sequence. Although both improvement techniques increased the seismic resistance of the embankment, the latter had a larger decrease in deformation and damage while retaining higher stability under simultaneous effects of seepage and earthquakes.
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