Putzmeister Concrete Pumps Help Plug Leaks Beneath Active Dam February 2004
STURTEVANT, Wis. (Feb. 2, 2004) – For the first time in its storied history, the U.S. Army Corps of Engineers is erecting a cut-off wall in front of an active dam, the Walter F. George Dam on the Chattahoochee River, which forms the border between Georgia and Alabama. Using Putzmeister concrete pumps, the wall is being built to eliminate seepage problems that have existed since a reservoir behind the dam was impounded in 1963.
A joint venture company called Treviicos/Rodio, Clearwater, Fla., was awarded a 36-month contract to build a secant-piled wall with more than 450 drilled shafts. Construction involves reverse-circulation techniques and boom pumps for the concrete placement. The wall will extend 300 feet into earthen embankments on either side of the dam.
Putzmeister 28Z- and 42X-Meter pumps supplied by H & L Concrete Pumping Inc., Troy, Ala., are placing more than 65,000 cubic yards of plastic mix concrete and flowing fill. September 2004 is the targeted completion date.
Background In an attempt to stop seepage during the 1980s, the Corps of Engineers installed cut-off walls in front of earthen embankments to the east and west of the dam. While this greatly reduced seepage under the embankments, water infiltration under the concrete structures of the dam continued.
Additional grouting also was conducted to plug concentrated water seepage, especially under the powerhouse, where peak flows were measured in excess of 30,000 gallons per minute.
When the seepage continued, the Corps of Engineers issued a contract for construction of a 24-inch-thick concrete cut-off wall in front of the dam and beneath the lock guide walls.
Cut-off formation A geological formation, through which the cut-off wall is installed, has three distinct layers. The uppermost layer is earthy limestone, followed by a layer of shell limestone/ sandy limestone. The hard, sandy limestone has a compressive strength up to 19,000 psi.
Immediately below is a layer of unconsolidated sand. The cut-off wall continues into this final layer at an elevation of –5.0 feet. With these conditions in mind, Treviicos/Rodio proposed using a combination of two methods to create the cut-off wall: secant piles using the RCD system for the concrete structure and slurry walls using a Hydromill along both embankments.
Secant piles In preparation for the secant piling, the lake bottom in front of the powerhouse, spillway and lock was dredged to remove debris and to form a minimum 6-foot trench for an underwater working apron.
Excavated to a minimum width of 7 feet, the trench was backfilled with flowing fill comprised of sand, cement, fly ash and water. A Putzmeister 28Z-Meter pump placed more than 6,000 yards of this material. The pump's 77-foot boom was fitted with a variety of different size tremie pipes that extended as far as 110 feet to place concrete.
Once the apron was completed, specially designed templates were installed on the dam's buttresses for casings to be guided through a collar and vibrated into the apron.
Two casing-mounted, reverse-circulation drilling rigs (Wirth PB612) are being used to install the secant piles. Each rig is positioned on the casings, which have a 54-inch diameter and are 130 feet in length. They are drilled to an elevation of –5.0 feet, approximately 230 feet from the top of the casing.
When drilling is completed, the pile is checked for vertical alignment against the adjacent pile. Concrete is then placed using a tremie pipe positioned within one-foot of the bottom of the pile. Concrete is placed to a level corresponding to the bottom of the lake. When placement is completed, the casing is removed.
The drill rigs are positioned using 200-ton cranes mounted on barges. Water depth exceeds 95 feet. More than 3,000 square feet of secant piles will be constructed in this manner.
And more than 450 piles will be bored, each 50-inch in diameter and spaced 33 inches from center to center. “By completion, we expect to have used 65,000 yards of concrete in the secant cut-off wall alone,” said Stefano Valagussa, deputy project manager.
Once the cut-off wall is completed, a 6-foot-thick pile cap will be tied into the dam structures to seal seepage from the top. H & L plans to use its Putzmeister 28Z-Meter to place the mix under 3,000 psi.
Diaphragm Wall by Hydromill The contractor has built a platform on the west embankment to permit installation of the cut-off wall by Hydromill. The wall will continue toward the embankment where the secant piles end and there will be a smooth transition between the new cut-off wall and the wall erected in the 1980s.
The platform area was initially sheet piled and filled to raise the level of the lake bottom to an elevation of 195 feet (59m). This involved an area more than 240 feet (71m) long, 30 feet (9m) wide and up to 60 feet (18m) deep, along with more than 5,000 cubic yards of flowing fill placed by the Putzmeister pump.
“H & L Concrete Pumping with their Putzmeister pumps have been a great asset to the project,” said Wesley Schmutzler, quality control/safety manager for Treviicos/Rodio.
H & L Concrete Pumping Inc. Formed in 1998 as a rental company specializing in concrete pumps, H & L Concrete Pumping has a fleet of seven boom pumps including five Putzmeister models.
The company took delivery of a new Putzmeister 42X in August 2003 and a 32Z in September to meet increasing rental demands for projects throughout Alabama, southern Georgia and Florida.
“The Putzmeister units are real smooth operating pumps,” said Keith Laney, H & L owner, “Since taking delivery of our first Putzmeister in 2000, they have proven very reliable with consistent, trouble-free use. The pumps have played a significant role in the high-profile, Walter F. George Dam project.”
JOB SPECS: Owner: U.S. Army Corps of Engineers General contractor: Treviicos/Rodio, a joint venture, Clearwater, Fla. Pumping contractor: H & L Concrete Pumping Inc., Troy, Ala. Ready-mix supplier: LaFarge North America Inc., Eufaula, Ala. Equipment: Putzmeister 28Z-Meter and 42X-Meter truck-mounted concrete pumps