GIVEN: 



Riprap 

 Filter 2 

 Filter 1 

 Embankment 



STEP 1: FILTER 1 GRADATION DESIGN 



D5o(FiLTER 1 ) < 40 X D50 (EMBANKMENT) = 8mm 



0.5mm = 5x Di5(EMBANKMENT) < D,5(FILTER1) <40 x Di5{EMBANKMENT) = 4mm 



Di5(FILTER 1) < 5 X Das (EMBANKMENT) = 2.5mm 

 SELECT Di5 = 1 .5mm, D50 = 3.0mm, Dgs - 6.0mm 



STEP 2: FILTER 2 GRADATION DESIGN 



D5o(FILTER 2) <40 x D5o(FILTER 1) = 120mm 

 7.5mm = 5xDi5(FILTER1) < D,5(FILTER2) <40x D,5(FILTER 1) = 60mm 



D,5(FILTER 2) <5 x D85(FILTER 1) = 30mm 

 SELECT Di5 = 20mm, D50 = 40mm, Dgs = 80mm 



STEP 3: CHECK FILTER 2 DESIGN AGAINST RIP-RAP 



DsolRIP-RAP) <40xD5o(FILTER2) 



5xDi5(FILTER2)< 

 100mm < 



500mm 

 Di5(RIP-RAP) 



300mm 

 Di5(RIP-RAP) 



300mm 



< 1600mm ^ OK 

 <40xDi5(FILTER2) 



< 800mm ^ OK 

 ^5xD85(FILTER2) 



< 400mm ^ OK 



STEP 4: SUMMARY 



ACCEPTABLE FILTER GRADATION DESIGN TABLE: 



FILTER 1 

 Di5(mm) 1.5 



D5o(mm) 3.0 



D85(mm) 6.0 



FILTER 2 

 20 

 40 

 80 



Figure C-4. Example of filter gradation design. 



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