Author: Gavi Sotelo, Solange Paihua
Conference: Tailings 2017: 4th International Seminar
Date: July 12-14, 2017
Collapsible soils are common in arid regions near the southern coast of Peru and often have a loose, metastable and brittle structure. They are usually of an eolian or alluvial origin with very low moisture content, negative pore pressures, and interparticle contacts that are partially cemented by salts. Thus, making them prone to sudden and substantial settlements and loss of shear strength by quenching of the negative pore pressures and dissolution of the salts if the moisture content is increased. Rapid rearrangement of the particles into a denser matrix can then occur causing the collapse phenomena. If kept dry and in their natural state they may remain metastable and can have moderate to high strength and stiffness. But in engineered applications, since these soils have physical and mechanical properties strongly influenced by moisture content, if wetting is a possibility, engineered mitigations must be adopted to either remove them or adequately accommodate their potential collapse.
The purpose of this paper is to present an estimate of the settlements that are expected to be experienced by a particular tailings dam founded on collapsible soils in southern Peru (case study). The estimates were made using a simplified approach based on the collapse index and collapse potential findings from laboratory testing (ASTM D5333) and were then corroborated by 2-D finite element numerical modeling using GeoStudio software. The results indicated that settlements in the order of 1.6 m could be expected at the time of start-up of the facility, which is the most critical period, when the supernatant water pond will be located against the dam and will lead to significant seepage and therefore wetting of the foundation materials.
Engineered solutions to mitigate the potential for settlement were adopted and included either excavating and replacing the soils with dense compacted fill or installing a geomembrane to substantially reduce potential wetting of the foundation.
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