Title:
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Design of hydraulic structures with plane intermediate filters
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Hydraulic structures should be secured against uplift pressure and
piping. Design engineers, therefore, may provide these structures with
different features such as intermediate filters to establish safer and/or more
economic structures. One or more intermediate filters can be built within the
floor. In this research, the problem of seepage flow beneath hydraulic
structures with two plane intermediate filters over a homogenous soil has
been deduced analytically using the conformal mapping technique. The
solutions include the potential heads at both key and stagnation points, the
hydraulic exit gradient just downstream the floor, and the location of the
stagnation points. The results have been used to create design charts over
a wide range of variables. Then, the general steady-state seepage problem
beneath a floor of hydraulic structure having any shape provided with any
number of filters and cut-offs located anywhere over a heterogeneous soil
has been obtained using a finite element model. After calibrating the model,
it has been applied to solve the same problem studied analytically using
conformal mapping to confirm both solutions and to determine the adequacy
of the numerical solution for potential heads, exit gradient and location of the
stagnation points. Good agreement between both solutions has been
obtained confirming the accuracy of the numerical solution. Then the model
has been used to check the stability against uplift and piping for New Esna
Barrage on Nile River in Egypt as one of the existing barrage, which has
been provided with one intermediate filter. After the stability of the barrage
against these forces has been confirmed, many alternative designs for its
floor have been studied to investigate where the exist solution from the
optimum one. These alternative designs include different lengths and
location for the filter and an upstream cut-off with different depths. Finally
the finite element model has been applied over a wide range of variables for
a comparison study between the effect of using one and two plane filters
upon uplift pressures, hydraulic exit gradients and seepage discharges
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