Ground Improvement for the Distressed Earth Bund Using Stone Column

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The paper describes the investigation and remediation of a distressed 7 m-high, 5.45 km-long earth bund built for a summer water-storage tank in Andhra Pradesh. During construction, cracks developed, parts of the downstream bund settled by up to 700 mm, and the downstream rock toe heaved by up to 175 mm. Further failures occurred despite a section being rebuilt with basal geosynthetic reinforcement.<br /><br />Investigations identified substantial variation in foundation soils, including soft to medium clay extending up to 8 m below the bund. Distress was concentrated where the cut-off trench had been excavated more deeply, indicating that local foundation conditions and trench depth had not been adequately accounted for during construction.<br /><br />Slope-stability analysis using TALREN showed a base-failure factor of safety below 1.0 under the assessed conditions. Stone columns were therefore proposed to strengthen the foundation and improve its shear resistance. The design used 800 mm-diameter columns in a triangular layout at 2.25 m spacing, extending to an average depth of 8 m beneath the bund and two rows beyond its downstream toe. Improved soil properties were estimated using the Priebe method and the GEOSTONECOL program. Reanalysis gave a factor of safety of 1.36 against base failure.<br /><br />The distressed reach was rebuilt after stone-column installation and was reported to be performing satisfactorily. The authors conclude that detailed understanding of subsurface conditions—and careful consideration of cut-off trench depth—is essential in earth-bund design, and that stone columns can be an effective remediation method.

Keywords

earth bund

foundation settlement

slope stability

stone columns

geosynthetic reinforcement

soft clay

cut-off trench

base failure

remediation

Andhra Pradesh