Concrete Chimney Shell Erection

CLIENT
Calaveras Power Partners

As part of the J.K. Spruce II Power Plant expansion at Calaveras Lake near San Antonio, Texas, Ibberson installed a 600-foot-tall tapered chimney stack.

Slipform technology was used to construct the chimney stack. Ibberson completed pouring concrete ahead of schedule and well within budget, thereby realizing a contract shared savings with our client.

The diameter of the chimney at the foundation was 62 feet and was reduced to 37 feet at the top. The wall thickness also varied throughout the pour as a design requirement. At the bottom, the wall thickness was 16 inches, then increased to 20 inches at the breaching openings, then reduced to 12 inches. A special steel slipform system was utilized to achieve these changes in diameter and wall thickness.

The chimney contains over 3,900 cubic yards of concrete and 488,000 lbs. of reinforcing steel. We started pouring concrete just before 9:00 a. m. on May 30, 2007 and finished just after 9:00 p.m. on June 29, 2007. During this time, the crews worked pouring concrete and placing reinforcing around the clock, seven days a week with only one scheduled four-day shutdown.

Ibberson’s crew mobilized and assembled forms to create a 3’-thick wall with a 6” setback at 152’. For nine days, the crew poured concrete 24 hours a day. Within six weeks from arriving on site, forms were stripped and the intake tower was completed.

The intake tower extends the full height of the dam and contains a series of vertically arranged slough gates that allow water to be tapped off at different levels. Ibberson’s design allowed the placement of the 4,000- to 6,000-lb. gates through 24’ x 14’ openings constructed in the upper deck, without having to shut down the slipform operation.