FNF Construction Inc. is using cement-stabilized alluvium (CSA) to channelize the Rio Salado's flow through Tempe, Arizona. By mixing portland cement, Class F fly ash, and native river bed (alluvial) soil, FNF is producing a CSA end product. While CSA is not new, using the extra-coarse alluvial deposits found in the Rio Salado bed is a new approach that offers increased durability and abrasion resistance.
To construct the levee with CSA, the channel bank is excavated, a terrace is shaped above the lower channel embankment, and a tapered embankment is above that. To protect the embankment, gabion mattresses are placed. First, a filter fabric liner is laid, then gabion mesh is unrolled over that. This mesh is shaped into baskets, which are filled with the 4- to 12-inch even gradation stone. Placement begins with the belly dumps, then the motor graders move in to the trench bottom. Steel-wheeled rollers follow the grader, making two or three passes over the CSA to achieve a 98 percent density. CSA placement for embankment protection continues in 9-inch lifts, each lift stepping back to conform to the 1:5:1 slope. The final step is backfilling the toe trench, channel bottom, and then the entire CSA levee structure with native alluvial soil.
