Failure Analysis and Strengthening of Tailing Pond Embankment by Prefabricated Vertical Drains and Geogrid-Paper

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An iron-ore tailings pond in eastern India required an embankment raise to increase storage capacity. During upstream construction in January 2014, a 200–250 m section of the embankment failed in a circular slip, with movement extending into the pond. Cracks and sinkholes continued to develop afterward, indicating ongoing settlement.<br /><br />Geotechnical investigations identified approximately 7.5 m of very soft, fine-grained tailings beneath the embankment. The tailings had low shear strength, very low permeability, and excess pore pressure from previous loading that had not dissipated. The embankment load exceeded the tailings’ estimated ultimate bearing capacity, explaining the failure. Ordinary consolidation was too slow for the mine’s schedule: achieving 90% consolidation was estimated to take about 5.7 years, while further raising was needed within months.<br /><br />The remedial design combined prefabricated vertical drains (PVDs) and geogrid reinforcement. PVDs, installed on a triangular grid at 1 m spacing, accelerated drainage and consolidation, helping the tailings gain strength under staged preload that formed part of the permanent embankment. Because the improved tailings’ bearing capacity alone remained inadequate for the planned load, two layers of high-tensile geogrid, separated by sand, were added for basal reinforcement.<br /><br />The combined system stabilized the existing embankment and enabled construction of an additional raise of up to 6 m. Settlement gauges and piezometers were installed to monitor settlement, consolidation, and pore-pressure dissipation. The case demonstrates that careful investigation and the appropriate use of drains and geosynthetic reinforcement can make further upstream raising feasible over weak tailings, even when operational constraints limit the time available for natural consolidation.

Keywords

iron ore tailings pond

embankment failure

upstream construction

soft tailings

prefabricated vertical drains

geogrid reinforcement

consolidation

bearing capacity

pore pressure dissipation

geotechnical stabilization