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<br />GEOIJEB/19ATTRESS SPILLWAY TESTS <br />Conducted by Simons, Li & Associates, Inc. <br />Fort Collins, Colorado <br />A diversion dam (six feet high, 16 feet wide, and 60 feet long) was <br />constructed in a creek at the outdoor laboratory at Colorado State University <br />to divert water from the creek to our embankment testing facilities. GEOWEB <br />(manufactured by Presto products, Inc.) and Reno mattress (manufactured by <br />t4accaferri Gabions, Inc.) were place side by side for protecting the diver- <br />sion dam spillway. The purpose of this arrangement was to compare a <br />soil/cement-filled GEOWEB against a rock-filled mattress structure under <br />various overtopping flow conditions. <br />The construction procedures for installation of the GEOWEB and mattresses <br />were as follows. First, a DuPont Typar 3401 geotextile (four ounce/yd2 <br />non-woven cloth) was laid on the surface of the spillway. The GEOWEB was <br />then placed directly on top of the cloth on the west half of the spillway, and <br />was filled with six inches of rock, one to three inches in size. A sand/ <br />cement mix of approximately one bag of cement to seven bags of sand was placed <br />over the too of the GEOWEB (see Figure 1) and compacted. On the east half of <br />the spillway, nine-inch mattresses were placed directly on top of the geotex- <br />tile. These mattresses were constructed by SLA crews utilizing normal proce- <br />dures, as outlined in Placcaferri literature covering construction practices <br />for Reno ~attresses. Rock ranging from three to six inches in size was hand- <br />placed according to the Maccaferri specifications. We found that the GEOWED <br />was easier to install and to control its quality of installation than the Reno <br />Mattresses. <br />Figure 2 shows the spillway was subjected to an overtopping flow <br />discharge of 60 cubic feet per second in July 1984. The unit-width discharge <br />was about five cfs/ft and the velocity on the spillway was about 22 fps over <br />the GEOWEB and about 15 fps over the mattresses because of the difference in <br />surface roughness. Under this condition, both the GEOIJEB and mattress struc- <br />tures performed well. However, because of the higher velocity at the toe of <br />the GEOWER portion of the spillway, Bone protective rocks (up to one foot in <br /> <br />