Question

The only provision among the following which can help control the seepage through the body of an earthen dam and thus to keep the phreatic line well within the dam width is _________________

(a) upstream impervious cut-off

(b) drain trench along the downstream toe

(c) relief wells

(d) chimney drain

The question was asked in a job interview.

This is a very interesting question from Rock Fill Dams in section Earthen and Rock Fill Dams of Irrigation Engineering

Answer 1

Correct choice is (d) chimney drain

Easy explanation: In case of large scale stratification a vertical filter is also provided along with the horizontal filter so as to effectively intercept the seeping water. This arrangement is nothing but is termed as chimney drain. It helps in keeping the phreatic line well within the dam body and also helps in rapid consolidation.