Question

What is the correct Douma’s equation for rectangular tunnels or conduits?

(a) X^2 + 10.4 Y^2 = d^2

(b) 4X^2 + 10.4 Y^2 = d^2

(c) 4X^2 + 44.4 Y^2 = d^2

(d) X^2 – 10.4 Y^2 = d^2

This question was addressed to me during an interview.

My question comes from Dam Outlet in chapter Pressure Conduits, Outlet Works through Dams and Rivers of Irrigation Engineering

Answer 1

Right option is (a) X^2 + 10.4 Y^2 = d^2

The explanation: Douma has suggested the following equation –

i. For circular conduits: 4X^2 + 44.4 Y^2 = d^2 where d is the diameter of the circular conduit

ii. For rectangular tunnels or conduits: X^2 + 10.4 Y^2 = d^2 where d is the width or height of the conduit depending on whether the sides or top and bottom curves are being designed. Where X and Y are the coordinates of any point on the curve and d is the width or height of the conduit.