A Geotechnical Study on Failed Base Slab of Molasses Tank: Fid-Bau Portal

A Geotechnical Study on Failed Base Slab of Molasses Tank

Kumar, Nandyala Darga / Lavanya, C.

Two molasses tanks of each 24 m diameter and 9.7 m high were built in the premises of Sugar Complex and Cogen Plant at Tumkur village, Shahpur Mandal, Yadgir dist., Karnataka. A 24 m diameter base slab of one of the molasses tanks was failed during erection of the steel tank and the other one started failing during the hydrotesting. To identify the factors that caused failure of base slab, an investigation was carried out by going through the site conditions, drawings and specifications of the work execution. The natural ground level (NGL) in the tank area is varying from 2.6 to 3.8 m deep from filled-up ground level (FGL). The tank finished floor level (FFL), i.e., top level of base slab of tank is 0.75 m above the filled-up ground level. A 24 m diameter RCC base slab of 150 mm thick was resting on a 350 mm circular RCC wall having 1.85 m strip footing and also on a central steel I Section (ISLB 350) having a square footing of size 2.15 m. The measured top surface levels of the failed 24 m diameter slab are same at the edge and central support portions, i.e., 366.875. In between edge and central support portions, the levels are 366.72 and 366.65. There is about 200 mm sagging noticed in the slab between the portions of edge and central support. In this paper, the reasons of failure of base slab are discussed based on the geotechnical investigations carried out in the filled-up ground within and outside the tank area. The natural ground possesses the required design bearing capacity, but the filled-up ground was not compacted as per the specifications furnished in the design report.