Straub, Lorenz G.Olson, Reuben M.2011-06-282011-06-281952-05https://hdl.handle.net/11299/108175Supplement I to Project Report No. 21; Tests on a Double Layer of Articulated Concrete MattressThe initial studies conducted on articulated concrete revetment at the St. Anthony Falls Hydraulic Laboratory during 1950 and 1951 were made with a single layer of revetment. The present tests were conducted with a double layer of mattress, placed one on top the other so that the interstices between adjacent blocks were symmetrically staggered. Test runs were made over a 32-ft length of a full-scale double mattress installed over a 15-in. sand bed in a 9-ft test channel with water depths of 2.1 to 3.2 ft and mean velocities of 3.2 to 10.0 fps. Turbulence was induced into the flow stream to simulate the random pressure pulsations which have been measured in revetted areas in the Lower Mississippi River. Pressure measurements indicated that the pressures at the bottom surface of the lower layer of blocks and in the sand beneath them remained essentially constant and that the differential pressures across the double mattress essentially followed the pulsating pressures above the top layer. No underscour of sand was observed after a total of 18.7 hr of test runs at a mean flow velocity of 5-1/2 fps. Some underscour was observed during a similar test at 8-1/2 fps, although pockets scoured and refilled. No settling of the mattress took place. Noticeable underscour occurred during a 1.2-hr test at 10 fps; yet, again, no revetment settling occurred.en-USReport