EM 111021100 (Part VI) Proposed Publishing （EM 111021100(第六部分)提出了出版）.pdfVIP

EM 1110-2-1100 (Part VI) Proposed Publishing Date: 30 Apr 03 (g) The underlayers should be at least three thicknesses of the W stone, but never less than 0.23 m 50 (Ahrens 1981b). The thickness can be calculated using Equation VI-5-119 with a coefficient of 3 rather than 2. Because a revetment is placed directly on the soil or fill material of the bank it protects, a single underlayer also functions as a bedding layer or filter blanket. f. Blanket stability in current fields. Stone blankets constructed of randomly-placed riprap or uniformly sized stone are commonly used to protect areas susceptible to erosion by fast-flowing currents. Blanket applications include lining the bottom and sloping sides of flow channels and armoring regions of tidal inlets where problematic scour has developed. Design of stable stone or riprap blankets is based on selecting stone sizes such that the shear stress required to dislodge the stones is greater than the expected shear stress at the bottom developed by the current. (1) Boundary layer shear stress. (a) Prandl established a universal velocity profile for flow parallel to the bed given by u 1 ln y %B (VI-5-123) v κ k ( s where κ = von Karman constant (= 0.4) y = elevation above the bed u = velocity at elevation y ks = boundary roughness B = function of Reynolds number (= 8.5 for fully rough, t