The presented article provides a comprehensive study on the stability analysis of earth-fill dams under rapid drawdown and transient flow conditions used to prepare stability analysis charts by conducting coupled finite-element numerical and analytical limit equilibrium procedures. In this regard, the impacts of different rapid drawdown conditions on the safety factor of the Alavian earth-fill dam are determined. The slope stability charts present for both shallow and deep slip surfaces with various permeabilities are verified by ground information obtained with extensive instrumentation on the dam’s site. The results showed that by decreasing the permeability of the core’s material, despite preventing seepage, the instability risk of the upstream slope as a result of rapid drawdown intensifies. Also, as stability charts can be stated, with increasing the slip surface’s depth and decreasing the hydraulic hydration, the reliability decreases, and the sliding surfaces’ sensitivity increases based on the drawdown rates, which have been revealed to be from 0.2 to 0.6, the most critical state for safety factors, showing significant declines.
Earth-dam failure starts with cracking in the clay core, and this cracking is not easy to detect and prevent. Therefore, swellable clay is a feasible solution, which helps to close the cracks automatically based on the self-healing process. The presented study utilizes experimental procedures to analyze the swelling behavior of fine-grained clayey soils to prevent structural failure regarding crack generations. In this regard, the clayey materials were modified using Kaolin and Bentonite mixed with various weight percentages (2.5, 5.0, 7.5, 10.0, and 12.5%) and extracted the geotechnical characteristics of the studied soils, which included 90 specimens and 85 tests, such as physical properties, consolidation, particle-size analysis, hydrometry, Atterberg limits, compaction, odometer, and pinhole. The experimental results revealed that the swelling of the Bentonite is more than Kaolin satisfied for self-healing features in clayey soils. Regarding the numerous swelling tests, Bentonite provides optimum results (attained 10%) compared to Kaolin. As a verification procedure, the pinhole test was performed on samples, which revealed that Bentonite was dominant in controlling the water flow through the samples.
Occurred damages on the bridge piers during earthquakes lead to significant financial losses worldwide every year and can cause social problems by disrupting traffic flow and transportation services. Rocking isolation of foundations is one of the damage reduction approaches to avoid structural damage on piers by transferring plastic hinges from piers to underlaying soil media. However, the behavior of rocking foundations on sands and clays has been studied comprehensively in past years; the behavior of these foundations on non-plastic silts has not been investigated well in the literature. In this research, the characteristic seismic behavior of a bridge pier considering rocking isolation is evaluated using small-scale physical modeling tests. To this aim, eight shaking table tests are conducted where both sandy and silty material are employed as the soil media. In addition to the effects of the underlying soil, the effects of the critical contact area ratio of the foundation and frequency of input motions are evaluated. Achieved results indicate that the considered bridge pier shows the same behavior trend for underlying silty soil and sandy one. However, because of the frequency-dependent behavior of silts and larger damping properties of such material, pier attracts lower accelerations and higher moments in non-plastic silty soil. Therefore, the achieved results show that the proposed design approaches of rocking foundations that are mostly extracted based on experimental studies on sands (or rarely on clay) can lead to non-conservative designs in silty soils.
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