An underground spring meanders beneath Patton Park in Southwest Detroit, making the soggy soil an undesirable site for the extensive sewer line work that's currently taking place.

General contractor Walbride-Aldinger and their subcontractors had to find a way to stabilize the soil for digging and boring operations, because they certainly couldn't go around the site. The area on the western end of the park already has a key pumping station, which is serviced by thousands of feet of buried 14- and 17-foot diameter pipe.

Over the years, the integrity of those pipes, which were installed in the 1950s, has not been an issue. But creating a soil shoring system for installing new sewer lines in the unstable soil would be difficult and risky business. Enter a California company called Raito, Inc. a specialist in "geosystems construction," which has brought to Michigan a specialized system of boring concrete pilings that has become fairly common overseas, but is rare in our state. Raito was hired by the project manager Walbridge-Aldinger.

The system involves the use of three side-by-side crane-mounted augers, which on this project are bored down to a depth of about 97 feet to reach "glacial till," a very stiff layer of stable soil that's above bedrock. As the augers descend and then come back up, cement slurry is pumped through the auger bits and combines with the soil in the ground to form a "soilcrete" piling that's not as hard as concrete - but is plenty strong enough to hold back a perimeter of soil to allow for safe excavation.

"This type of soil stabilization is relatively new in Michigan," said Raito Senior Project Manager David Miller. "It's like a big egg beater. The idea is not to take the soil out, but to blend it in place, and that's a relatively new process. The process is also unique in that it allows construction in places with high groundwater, limited space or in other areas that in the past you wouldn't typically see construction."

The cement slurry is mixed at a batch plant on the site, and is pumped several hundred feet away to the rig running the augers. The three-foot diameter augers are placed two feet part on the rig, and when their work is done in January, they will have left 3,600 soilcrete pilings. The pilings are left in place and will remain buried on the 12-acre construction site.

"I was surprised at how hard the pilings get," said Walbridge-Adlinger Project Manager Brian Cruickshank. "It made a believer out of me."

The 350,000-lb crane sits on metal sheets so that it won't sink in the ground. Raito is one of only a few companies that performs this kind of work, and has only about 10 such rigs in the nation, and another 50 around the world.

Miller said the multi-auger process was invented about 15 years ago and is commonly used in Asia. He said the process can be 15-30 percent cheaper than driving conventional sheet pilings, and the work will usually get finished faster.

The entire $62 million project, which involves the installation of 5,400 lineal feet of 72-inch diameter pipe, is being undertaken to separate sewage from storm water in this part of Detroit, which currently travel through the same pipes. This part of the system serves about 11,000 acres of Detroit. Currently, when it's not raining, sewage is screened and treated properly and is dumped safely into the Rouge River. But during heavy rains, the system is overwhelmed, and is designed to move untreated sewage directly into the Rouge River.

When the new system is in place, a new treatment plant that will be built on the Patton Park site will screen solids from the sewage and partially treat it with chlorine. During heavy rains, the pipes or "barrels" in the new system will contain the overflow and act as holding tanks until a sewer treatment plant at the end of the line can further process the wastewater before it is released.

When the job is done, Patton Park will look like its former self - and part of the project includes the $10 million renovation of a nearby city recreation building.

"The tradespeople are doing a lot of work out here, and when we're finished, no one will ever see it again," said Cruickshank. "So it's nice that they get a little recognition. They're doing a great job."

OPERATING ENGINEER Matt Newman operates a three-bit drill that makes "soilcrete" shoring columns under Patton Park in Detroit.

A GASKET is placed around a 72-inch diameter sewer pipe by Danny McCoy of Laborers Local 1191.