Application of Deep Mixing and Stone Column Techniques for stabilization of Large Earth Cum Rock Fill (ECRF) Dam for an Irrigation project-Paper

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The Polavaram irrigation project in Andhra Pradesh, India, includes a 1,750 m-long earth-cum-rock-fill (ECRF) dam. To improve foundation performance and limit differential settlement, the design combines deep soil mixing (DSM) columns near the plastic-concrete cutoff wall with vibro stone columns beneath the wider dam footprint. DSM provides an intermediate ground stiffness between the stiff cutoff wall and the stone-column-treated areas, creating a gradual transition toward the dam toes.<br /><br />DSM mixes in-situ soil with cement-based binder to form stronger, stiffer soil-cement columns. Project requirements target a fivefold increase in soil stiffness from DSM, compared with a twofold increase for stone columns. Field trials were planned to determine suitable binder mixes and installation parameters, and to verify column strength and stiffness through sampling and laboratory testing. The stated 28-day characteristic unconfined compressive strength target is 0.5–1.0 MPa.<br /><br />The design includes a 10 m transition zone with five rows of DSM columns, progressively reducing treatment stiffness and column depth toward the stone-column area. Plaxis 2D analyses assessed settlement during staged construction, including dam loading before and after upstream water filling. Indicative maximum settlements for the lower-bound stiffness case were 48 cm before filling and 50 cm afterward; for the upper-bound case, they were 46 cm and 48 cm.<br /><br />The study presents DSM as a sustainable alternative or complement to conventional ground improvement. It can reinforce the dam foundation and protect the cutoff wall while reducing the stiffness contrast between treatment zones. Field-trial results are intended to guide final construction parameters and confirm that the specified performance can be achieved.

Keywords

Polavaram irrigation project

Andhra Pradesh

earth-cum-rock-fill dam

deep soil mixing

vibro stone columns

foundation improvement

differential settlement

soil-cement columns

Plaxis 2D analysis

ground improvement