A Geotechnical Study on Breached Summer Storage Tank

Abstract

This paper presents some of the observations made as well as geotechnical testing carried out in search of reasons of breached out summer storage tank, which was about to be commissioned for supply of water especially during summer season to the villagers of Nuzendla mandal in Andhra Pradesh. The tank has about 10 acres of storage area and the levels of water in the tank are not the same throughout the area but varying from 3 to 5.5 m. The breaching of tank was occurred, at a location where the water level is 5.5 m high, and where two mutually perpendicular bunds are joining. The disturbed and undisturbed soil samples collected from the location where breaching of tank took place were tested in the laboratory to understand the basic characteristics of the soil used for bund construction. The grain size analysis, compaction control, free swell index, liquid and plastic limits, permeability and shear characteristics are determined. It is noticed that the locally available soil is used for bund construction and it is of medium to high plastic in nature. The compaction levels at certain places are found to be inappropriate and the slopes of bund throughout are not as per the specifications. The filling up of water into the tank was done at a time, but not in stage by stage filling process. The reasons of breaching of earth bund are noticed as erosion of soil due to windblown water wave action, not providing the revetment on upstream slope and required slope as per the specifications.