'Robust' Rebuild Designed to Deliver Reservoir 2.0
Further encircling the facility's base is a 25-ft-wide toe buttress that varies from 10-18 ft in thickness. Or as Dreese calls it, "just a honkin' big section of soil cement." Seriously, he explains, the toe buttress adds stability for a rapid or emergency drawdown.
Instead of end dumps, Kiewit used Caterpillar 740 ejector trucks to feed roughly 12 cu yd of soil cement—about 6 cu yd at a time—to a GPS-controlled D6 that dozed it into place, with lift depths ranging from 8 to 12 in. At its most productive, the contractor's fleet peaked at 13 trucks, for an estimated placement of 5,000 cu yd per shift, says Watkinson. Crews placed some 120 miles of soil cement for the toe buttress.
Next, instead of flat-plate soil cement, Kiewit added back a stair-step soil cement system. (The original reservoir featured stair steps along the upper sections.)
For this placement, the ejector trucks fed the same soil cement material to a pair of conveyor systems. A dozer with spreader box placed the no-slump soil cement in 7 ft widths. After starting with 6-in. lifts, the crews settled into placements of 8-in. lifts.
Per shift, crews placed an average of about 1,000 cu yd, or about 10,000 lineal ft, says Watkinson. In all, the effort required 211,000 cu yd of material to produce the stair steps, which numbered as many as 83 in sections and collectively amounted to 250 miles. Crews bonded the stair steps with a cement slurry.
Whereas the flat-plate system measured 16 in. deep, the staggered stair step—with an exposed tread width of between 9 and 12 in.—results in a thickness of up to 33 in., says Watkinson.
Also, Dreese explains, compared with a flat-plate design, the stair steps help minimize wave action. At the same time, the thickness will provide sufficient strength over the 50-year design life, even if the stair-step profile becomes worn down over time.
A 2-ft-thick section of roller-compacted concrete, placed via two 1-ft-thick lifts, tops the stair steps. On top of that, crews are installing precast concrete seawall sections measuring 3 ft 6 in. tall.
Kiewit-Gannett Fleming says construction is on schedule for a November completion, with the state of Florida potentially allowing Tampa Bay Water to begin refilling the reservoir in late July or August. After that, for the project team and the utility, it's a five-year test of the rebooted reservoir.