Design of Slope Protection Works in the Third Reach of Vadakara-Mahi Canal

This paper presents a case study of design of slope protection works in the third reach of Vadakara-Mahi Canal in Northern Kerala. The canal has a length of 17.61 km, and the construction works in its third reach have been stalled due to the loose nature of soil and collapsing sides. As the alignment of canal in this reach passes through hillocks and elevated terrains, the depth of cutting involved is very high up to a maximum of 24 m. Many residential buildings are situated on both the banks of the canal, and hence the retaining system and construction methodology adopted should not pose any risk to the safety of these structures. Geotechnical investigation is carried out by drilling six boreholes by rotary boring method. In the first tier, an anchored secant pile wall of height 12 m above the canal bed level is designed, and the passive pressure in front of the wall is enhanced by providing geobags filled with locally available soil. The backfill soil in front of the anchor block is stabilized to improve the passive resistance. In the second tier, a gabion faced retaining wall is designed. For the third tier, a stable slope of height 3 m is designed above the gabion wall, and coir geotextile is provided for erosion control. The global stability is checked by carrying out finite element analyses with the software PLAXIS 2D. The distribution of bending moment and shear force in the secant pile obtained from finite element analyses is used for the structural design.