Question

According to Terzaghi, the ratio of D15 of filter to D15 of base material should be _____________

(a) > 5

(b) < 4

(c) 4 to 5

(d) < 5

The question was asked in a dream while sleeping

My doubt is from Rock Fill Dams in division Earthen and Rock Fill Dams of Irrigation Engineering

Answer 1

The correct choice is (c) 4 to 5

The explanation is: Terzaghi provided a rational approach to the design of filters. The following filter criteria should be satisfied-

D15 of filter / D85 of base materials < 4 to 5 < D15 of filter/ D15 of base materials

The filters should be such that neither the embankment nor the foundation material can penetrate and clog the filters.