Atlanta’s Largest Tunneling Project Features Concrete Pumping and Placing Versatility
Atlanta’s Largest Tunneling Project Features Concrete Pumping and Placing VersatilityWest Area Combined Sewer Overflows (CSOs) Tunnels and Pumping Station project makes a mark on history
ALLENTOWN, PA (February 1, 2008) – Major changes in state and federal regulations, that occurred after Atlanta, Georgia completed its Combined Sewer Overflow (CSO) control program, was the impetus for the city’s largest tunneling project to date, the West Area CSO Tunnels and Pumping Station. Presented with the challenge of helping construct two deep tunnels that will have a combined length of 43,800 feet and are anywhere from 160 – 320 feet below ground level, Atlanta CSO Constructors (ACC) knew its Putzmeister concrete pumping and placing equipment would be invaluable.
Bursting at the Seams
Comprising the Clear Creek Tunnel and the North Avenue Tunnel, this historic project was prompted by increasingly stringent regulatory controls on water quality across North America, according to Ken Johnston of the City of Atlanta (the owner/developer for this project). This has resulted in municipal governments, such as Atlanta, investing heavily in infrastructure to control CSOs (when combined sewers exceed their conveyance capacity during periods of heavy rainfall or snowmelt).
Atlanta’s population is now over 450,000 with a sewer system servicing 1.2 million (including adjacent jurisdictions). The city has a Combined Sewer System (CSS) encompassing about 15 percent of its total 2,200 miles of sewers, according to Johnston.
“In the 1990s, the City constructed a series of CSO control facilities which provided screening and chlorination at seven CSO discharge points across the CSS watershed. Those facilities were adequate to meet water quality regulations in effect at the time they were constructed, ” says Johnston. “But as the water quality regulations for CSOs were changed, the federal EPA deemed the water quality standards for metals were being violated by these discharges and a suit was brought against the City to force a higher standard of compliance,” says Johnston.
Consequently, Atlanta entered into a federal Consent Decree which would bring CSOs into compliance with federal standards by 2007. The City has completed all required CSO improvement projects except the West Area CSO Storage Tunnel and Pumping Station which is on schedule. Due to delays beyond the City’s control on the West CSO Storage Tunnel and Pumping Station project, and because of the City’s excellent record in achieving compliance with all other CSO milestones, the EPA and Georgia EPD granted a one-year time extension to November 4, 2008 for the project.
“The design and construction of the West Area CSO Tunnels and Pumping Station is a vital element of this plan,” says Johnston.
In 2003, to make Atlanta’s largest tunneling system a reality, the City’s Department of Watershed Management chose Jordan, Jones & Goulding, Inc/Delon Hampton & Associates/Hatch-Mott McDonald, Joint Venture (JDH) as the design engineer and ACC, a joint venture of Obayashi Corporation (Obayashi) and Massana Construction, LLC, as the general contractor and the concrete pump and mix supplier for the project.
ACC arrived on-site to commence construction on the project in July 2004.
“This project was designed to capture combined sewage overflows from three of the Atlanta’s existing CSO facilities on the northern end of the CSS watershed,” comments Darrell Liebno, assistant project manager for ACC.
The design of this massive project includes two connected tunnels that will convey the wastewater originating from the North Avenue, Clear Creek and Tanyard Creek CSO facilities to a submersible pumping station located adjacent to the R.M. Clayton Water Reclamation Center (WRC), according to Liebno.
The Clear Creek and North Avenue Tunnels were excavated using two hard rock Tunnel Boring Machines (TBMs). The excavated diameter for the tunnels were 27 feet with a 24-foot diameter of unreinforced concrete lining, constructed in areas where required for permanent support as well as to control long-term groundwater inflows.
Access for tunnel construction is being provided through 40-foot finished diameter construction shafts located at each end of the two TBM tunnels. There are four construction shafts; the Rockdale, R.M. Clayton, Clear Creek and North Avenue Construction Shafts. The shafts range in depths from 160 to 320 feet.
Serving It Up Two Ways
Acting as the concrete pumping and placing supplier as well as the concrete mix supplier, gives ACC more flexibility and control in choosing how to deliver and place the concrete for each tunnel.
“What makes this project unique is that for each tunnel’s concrete linings, we’re delivering concrete to each of the tunnels two different ways,” says Liebno. “For the Clear Creek Tunnel we’re delivering the concrete completely underground versus the North Avenue tunnel where we’re using ready mix trucks and pumps located above ground to deliver the concrete underground.”
There is reasoning behind pumping and placing the concrete for the two tunnels, two different ways, according to Liebno. “The North Avenue Tunnel’s concrete was delivered from the surface because the tunnel was accessible from the road via down-holes. Logistically this was simpler than transporting concrete to a shaft, down the shaft and to the forms,” notes Liebno. “This type of access was not available for the Clear Creek tunnel; therefore concrete had to be batched on the surface, conveyed underground and transported to the forms.”
According to Liebno, ACC’s team worked closely with Putzmeister America’s team consisting of, Bill Carbeau, Director - Special Applications Business and Bob Lieberman, Special Products Sales Manager, to develop and plan the two different methods of delivery and placement of concrete for the two tunnels.
“Bill and Bob always make themselves readily available if we have any questions or concerns, they’re reliable,” says Liebno. “Their combined expertise on their equipment and technologies helped us tremendously in planning out this project.”
“It’s always rewarding working with Obayashi on their projects. We enjoy working with them and look forward to many more years of work together,” notes Carbeau.
To help “serve up” the concrete two separate ways, ACC installed two types of Putzmeister concrete pumping and placing equipment at the site in July 2007. The equipment includes: one rail-mounted, electric-driven BSA 1409 trailer pump; two rail-mounted electric-driven BSA 2109H trailer pumps; one trailer-mounted, diesel-driven BSA 14000 trailer pump and two TSV 5-12 Snorkel concrete placing systems.
In addition, ACC also has Putzmeister Hydraulic Diversion Valves and Hydraulic Shut-off Valves that are being used on the North Avenue Tunnel where concrete is being pumped from the surface. The shut-off valve is located underground, directly beneath the down-hole and the diversion valve is located on the surface. The diversion valve is used in conjunction with a Putzmeister PVT 710 Big Blue® ball valve style pump to clean out the concrete slick line from the pump to the forms.
To help place concrete as efficiently as possible for both of the tunnels linings, ACC chose to batch the concrete mix themselves on-site via a mix plant.
For the Clear Creek Tunnel’s concrete linings, according to Adam Stremcha, project engineer for ACC, the concrete is delivered via an underground method:
-Above ground, the concrete is discharged onto a conveyor once it has been batched. The conveyor then transports the concrete approximately 100 feet to the construction shaft.
-In the construction shaft, the concrete is dropped 300 feet by gravity through a 10-inch diameter steel pipe and transported to a holding hopper at the bottom of the shaft.
-Once the hopper is filled, a train consisting of three-each transport cars is loaded and hauled through the tunnel to the concrete discharge bridge.
-Using the conveyors on this bridge, the concrete is discharged from the three cars simultaneously and into a remix hopper.
-From here, the concrete is discharged into the BSA 2109H and pumped through five-inch slick line to the TSV 5-12 Snorkel for placement into the forms.
For the North Avenue tunnel, according to Stremcha, concrete is delivered via an above ground method:
-The concrete is batched by the mix plant into ready mix trucks.
-Then, the concrete is transported via the ready mix trucks to the BSA 14000 trailer pump located above ground where a down-hole has been installed.
-The concrete is pumped by the BSA 14000 through the down-hole via slick line to the TSV 5-12 Snorkel.
-The TSV 5-12 Snorkel then places the concrete into the forms.
“The TSV 5-12 Snorkel made our job a lot easier,” notes Stremcha. “The over-pressure control unit of the machine prevents damages of the formwork; it retracts automatically if the concrete pressure exceeds the adjustable limit between 14.5 – 145 psi (1 to 10 bar).
“In addition, the TSV 5-12 Snorkel has an elevating platform at the nozzle section of the unit,” adds Stremcha. “This allows the machine to reach the feed pipe on the top of a form.”
The TSV 5-12 Snorkel is placing the concrete at 60 cubic feet per hour.
Sizing Up the Equipment and the Concrete
To date, ACC has pumped and placed 35,000 cubic yards of the total 120,000 cubic yards of concrete needed with their Putzmeister equipment, which includes the concrete placed for the Clear Creek and North Avenue tunnel concrete linings. The combined total concrete needed for both tunnels’ linings is about 100,000 cubic yards of concrete, according to Liebno. The remaining 20,000 cubic yards of concrete will be placed in the shaft bottoms and linings. The TSV Snorkel machines will not be used for this section; however the BSA trailer pumps will be used. The grand total of concrete needed for this project is 155,000 cubic yards.
The remaining 35,000 cubic yards of concrete not placed by the TSV Snorkel units and BSA trailer pumps, was placed by a sub-contractor to ACC, Pioneer Concrete Pumping (Pioneer). Used for the four construction shafts and open-cut intakes, Pioneer’s Putzmeister truck-mounted boom pumps, ranging from their 32Z- to their 63Z-Meter, were on hand to place the concrete. Pioneer has been on the job site periodically since late 2004.
Liebno and Stremcha say both their TSV Snorkel placing systems and the BSA trailer pumps are displaying their muscle on-site.
“The two TSV 5-12 Snorkel machines have been very dependable,” notes Liebno. “The machine rides on rails set into tunnel formwork and can turn the telescopic snorkel pipe 360° rectangular to the formwork axle. It’s driving length of 49' 3" has also been a huge asset to us on this job.”
“For the North Avenue Tunnel concrete linings, the BSA 14000 is pumping a remarkable 2,800 feet via slick line,” comments Liebno. “It’s high line of pressure of 3,190 psi and high output volumes of 133 yd3/hr has benefited us greatly, given the long distances the project requires the concrete to be placed.”
Stremcha notes, “The electrically-driven BSA 2109H is rail-mounted which allows for high mobility in the Clear Creek Tunnel. Using electric power, this machine is also environmentally friendly in its underground surroundings by giving off zero emissions.”
Liebno says Obayashi Corporation, independent of ACC, has used their Putzmeister pumping and placing equipment on other various tunneling projects. Most recently is the Nancy Creek Tunnel back in 2005 in Atlanta, where both BSA 2109H and BSA 1409 trailer pumps were used as well as their TSV 3-6 Snorkel machine.
“Overall, what’s so beneficial in using Putzmeister and Allentown’s equipment is that their TSV Snorkel placing systems can provide more volume and more pressure than other comparable equipment,” notes Liebno. “Putzmeister and Allentown can supply both the trailer pump and the placing system. Their trailer pumps offer both diesel and electrical versions, and their TSV Snorkels offer three different sizes. They give us a lot of choices, not just one.”
According to Liebno, the concrete mix being placed for the concrete linings of both tunnels is not overly harsh. “The mix contains 67-pound stone, natural sand, flyash, cement as well as admixtures,” says Liebno. “The BSAs and Snorkels handle the 4,000-psi mix with ease.”
Pushing Forward to the Finish Line
“With Putzmeister America recently acquiring Allentown, the two companies have combined their expertise and technologies to offer a stronger and more comprehensive presence in the underground industry for customers such as Obayashi,” comments Carbeau. “We’ve been working with them for 10 years helping them find the best solutions for their specific project needs. Now we’re equipped to provide them, and the rest of our customers, with even better solutions and technologies than before.”
Putzmeister and Allentown’s full line of equipment in their Underground line are:
•GM-060 Rotary Gun
•PD-1/GRH Gunning Rig
•PD-1 Continuous Pre-dampener
•Powercreter® 10 and 20
•A10 and A20 Peristaltic Chemical/Accelerant Dosing Pumps
•PM 407 and 500 Remote Control Nozzle Carriers
•BSA 1409, 2109, 2110 and 14000 trailer pumps
•TSV 2-4, 3-6 and 5-12 Snorkel placing systems
•JT Jumbo 3,000, 5,000 and 10,000 Troughs
To learn more about Putzmeister and Allentown’s full line of Underground equipment, visit www.allentownshotcrete.com.
Along with the two tunnels that are being constructed as part of this project, a separate treatment plant for the tunnels is being built as a result of most of the effluent stream consisting of storm water.
With 35 percent of the concrete linings for the two tunnels complete, the project is on schedule for its November 2008 deadline.