Application of Deep Mixing and Stone Column Techniques for Stabilization of Large Earth Cum Rock Fill (ECRF) Dam for an Irrigation Project

A Large Earth Cum Rock Fill, ECRF Dam, is under construction at Polavaram in the state of Andhra Pradesh in India as part of an irrigation project. The Embankment crest width of the dam is 12.5 m and the base width is approximately 136.75 m with a stepped sloping height of 27 m on both upstream/downstream sides. Once the 1.2 m Thick Plastic concrete cutoff wall is constructed below the dam along the longitudinal central axis to avoid seepage, this magnificent structure will be supported on a series of Deep Mixing Columns and Stone Columns that are evenly arranged under the footprint of ECRF Dam forming a smooth transition of gradually reducing stiffness moduli of treated ground from the centre of the embankment, where the foundation stresses are high, towards the edges in order to be able to progressively limit the settlements under the dam to a specified allowable limit. As such, the required post-treatment stiffness in the case of stone columns is 2 times the in situ stiffness of foundation soil, whereas it is expected to be 5 times the improvement for Deep Mixing as per project specifications. Laboratory testing and Field Trials were undertaken successfully to verify the design.