Question

The minimum thickness (t) of the downstream floor required in the design of weir can be expressed by the equation ___________

(a) h / (G+1)

(b) (h-t) / (G-1)

(c) h / (G-1)

(d) 1.33 h /(G-1)

I have been asked this question during an interview for a job.

My question is from Seepage Theories topic in portion Seepage Theories and Weirs and Barrages Design of Irrigation Engineering

Answer 1

The correct answer is (c) h / (G-1)

For explanation: As per Bligh’s theory, the thickness of D/s floor is expressed as h/(G-1) where h = ordinate of the H.G line above the top of the floor and G is the specific gravity of the floor material. To allow a suitable F.O.S  this value is generally increased by 33%.