Abstract:
Ground water reservoirs are vastly used in water supply schemes for water storage. Both fixed
base and retaining wall type structural arrangements are used in those without any basis, where
mostly the selected arrangement will depend on the preference and the experience of the design
engineer. The aim of this study is to develop a framework to select a proper structural
arrangement for ground water reservoirs depending on the wall height and the capacity of the
tank for an economical design with adequate structural capacity. Objectives of this research are
analysing the ground water reservoirs with fixed base and retaining wall type base, designing
structural components using available design standards and comparing results considering
reservoir capacity and wall height. Most common rectangular shaped ground water reservoir
capacities in Sri Lanka were studied. Finite Element Modelling (FEM) and theoretical analysis
were used to study the structural behaviour of ground water reservoirs, and spread sheets were
used to design structural components. Results obtained from this study were compared with an
existing ground water reservoir. It was evident from the results that fixed base type arrangement
is economical for all the wall heights of reservoirs having capacity up to 225 m3. For capacities
between 225 m3 to 2000 m3, retaining wall type arrangement is economical for wall heights
up to about 7 m, while fixed base type arrangement is economical for wall heights beyond 7
m. Overall, retaining wall type arrangement becomes economical for larger wall heights when
the capacity increases. According to results presented in this paper, it is evident that selection
of the base type (fixed base or the retaining wall type base) in a water retaining structure should
be carefully done by considering the tank capacity and the wall height. Since this research was
done for a length to width ratio of 1, further research should be done for different length to
width ratios to check the validity of these conclusions. Further, this research was carried out
using BS standards as the design practice. Therefore, this research can be extended using
Eurocode to check the possibility of further optimisation of both structural arrangements.
