Geotechnical Risk and Environmental Impact: the Stability of Phosphor- Gypsum Embankments in SW Spain

Abstract

This research analyzed geotechnical risk and environmental impact by studying the stability of phosphor-gypsum stacking which could lead to embankment failure, due to the failure of underlying soil materials (soft soil composed of marsh mud). Such an event could cause the outflow of a large volume of toxic acidic water and radioactive isotopes, which would signify a great pollution risk for the Marismas del Rincón of the Tinto River (Huelva, Spain). This study consisted of six CPTU static penetrations by rotary drills with continuous sampling. Laboratory tests were then performed to identify the samples and analyze their mechanical properties. The results obtained showed factors of safety (FS) with a value greater than one, both under normal conditions (no seismic event) and also under extreme conditions when there was a seismic event and a maximum load. When a staged load was modeled, the resulting FSs were found to exceed 1.6. Regarding consolidation settlements, when the most unfavorable mud thickness layer (25 m) was considered, a period of 3.2 years was required to reach 90% of the expected consolidation. The sloping phosphor-gypsum stacks were found to be stable in regards to the potential failure of the underlying soil materials. Furthermore, the low deposit rate (0.20 T/m2/month equal to a phosphor-gypsum quantity of approximately 11 cm/month) contributed somewhat to the dissipation of interstitial pressures that could potentially arise, and was consequently a further guarantee of stability