Low cost underground water tanks

There is a great need to construct low cost underground water tanks in the dry zone of Sri Lanka to enable rain water harvesting .A research is conducted to introduce the said tanks with the use of low cost materials. Mainly brickwork and ferro-cement were considered in the study. The approach is based on analytical results obtained from a computer program and experimental investigation of properties of the construction materials. The computer program was developed to analyse shell type tanks by incorporating the linear elastic theory of shells. Mainly two types of cylindrical tanks with spherical domed roofs were analyzed; viz. "Normal type" and "Advanced type". The difference between the two types is the bottom shape. The normal type tanks are having a flat bottom and the advanced type tanks with an inverted spherical domed bottom. Both fully underground and partially underground tanks were analysed. A parametric study was carried out by using the computer program. The results revealed that the maximum tank diameter that can be achieved by using brickwork for the spherical roof and the cylindrical wall of the tanks is only about 2.0 -2.4 m which resulted in an approximate tank capacity of 10m3 . The governing factor in deciding the capacity is the flexural strength of brickwork. Hence, brickwork reinforced with wire mesh is considered for the cylindrical wall. The experimental investigations revealed that the flexural strength could be increased dramatically with this new composite construction material. The new composite material is named as "Brickwork Reinforced with Wire Mesh (BR WM)". According to the results of the parametric study maximum tank diameter that can be achieved for a partially underground advanced type tank having a ferro-cement spherical roof, BRWM cylindrical wall and a ferro-cement inverted spherical bottom is about 6 m which resulted in an approximate capacity of 100 rrr'. The structural design for a 66 rrr' tank having the above-mentioned specifications was completed