Abstract:
Southern Petrochemical Industries Corporation Ltd has constructed two reservoirs to meet the demand of water for industrial purpose. In recent times one of the reservoir has reported loss of water probably due to seepage.
To identify the seepage zone inside the tank, the geological, geophysical, hydrogeological and sedimentological studies were carried out. With the above aim, piezometric wells to monitor the water heads were erected and monitoring of piezometric water heads in the wells was continued for two weeks. From the observations, it is found that increase of water head ('A' type) in certain profiles and decrease of water head (Q type) in some profiles and intermediate types are also recorded in the profiles of the study area. The increase of elevation head are called as 'A' type, decrease of elevation head as K type and intermediate types as H and Q types of piezometric surfaces. 'A' type of piezometric surface are having deeper water table than the Q, K and H types.
Identification of seepage points inside the tank by utilizing the variables like piezometric water head differences in the wells, distances of the wells from the tank, depth of soil column in each wells, water level in the tank. Analysis reveals the distances of the seepage inside the tank. Higher concentration of seepage points of found within the distances of 20-30 m from the bund of the tank. 'A' types of piezometric surface are called vertical seepage and other K, H and Q types of the piezometric profiles are called as horizontal seepage. This is because the elevation of water head for the horizontal seepage, the points are identified in close proximity to the bund of the tank, whereas for the 'A' types, of piezometric wells, the seepage points are found to be distributed in the longer distances from the bund.
The percolation of water increased the intergranular pressure in the subsurface condition. Since 'A' type of piezometric surface are found in the homogenous and permeable formation, as a result the velocity of the water flow is reduced. The reduction of velocity increased the water head from the source outwardly. In the zones of K and H and Q types, the pressure heads in the piezometric wells are decreasing. The head losses are due to the internal and external friction. Seepage points identified inside the reservoir were checked physically after dewatering of the reservoir. Wherever these points were marked in the layout, there were conical shaped depressions in the sand bed. These conical depressions were created due to the seepage of water through the polypropylene sheets. The computed seepage points and actual seepage points were corroborating with each other. Authority removed the sand bed and sealed the damaged sheets, then seepage was completely stopped.
