Question

The seepage forces within the filter are controlled up to permissible small magnitudes when the ratio of D15 of filter to D15 of base material is ___________________

(a) between 5 to 40

(b) less than 5

(c) between 5 to 20

(d) less than 4

The question was asked in a dream while sleeping

Query is from Rock Fill Dams in chapter Earthen and Rock Fill Dams of Irrigation Engineering

Answer 1

Right answer is (a) between 5 to 40

Easy explanation: When the ratio does not exceed 4 to 5, the base material is prevented from passing through the pores of the filter. When this ratio is more than 5 and less than 40, the seepage forces within the filter are controlled up to permissible small magnitudes.