Rentals Ease Emergency Sewer Work
Baltazar Contractors, Inc. drives and braces sheet piles, encases new pipe in concrete under Route 120, Southington, Conn.
By Paul Fournier
Construction crews had to install permanent steel sheet piling and encase a replacement pipe in concrete during emergency repairs of a collapsed sewer interceptor under a state highway in Southington, Conn.
Baltazar Contractors of Ludlow, Mass., has a contract with the two to install about 250 feet of 24-inch PVC pipe parallel to a reinforced concrete pipe that had become blocked near Rout 120 (Meriden Avenue).
"Apparently, a section of the concrete pipe collapsed, blocking the line," said James Gura of the Southington Engineering Department. He said the exact cause of the failure of the section of 42-year-old pipe was undetermined. Officials called Baltazar Contractors to make emergency repairs.
"We have done sewer work for the town in the past, and they knew that we had the proper equipment and the 
expertise to make the repairs," said Gene Zwicharowsky, Baltazar project superintendent and a 20-year construction veteran who is directing the work crews. Zwicharowsky works closely with the company's project manager, Bob Simard.
During construction, the partially blocked existing RCP interceptor has remained in service since it can handle normal flows. However, if flows exceed interceptor capacity, two rented Godwin Dri-Prime Silenced 8-inch pumps kick in and send the sewage overflow through two temporary bypass lines, said Zwicharowsky. In addition, the contractor has rented three, 3-inch Godwin submersible electric pumps to dewater pipe trenches. Furthermore, he said that Godwin is poised to install a wellpoint system for a portion of trench excavation near a local brook.
Because of poor soil conditions and the proximity of Misery Brook, project engineers Sefert Associates of Naugatuck, Conn., called for the installation of stay-in-place sheet piling along the entire section of 20-foot deep trench and three new manholes. Sefert worked up a method of installation and bracing with Mabey Bridge & Shore, Inc.
To drive the sheet piles, Baltazar used one of its Cat 345B excavators equipped with a Dawson EMV400 vibratory hammer rented from Mabey Bridge & Shore, Inc. The hammer, which is actually a hydraulic clamp and vibrator attachment, replaces the excavator bucket and is ideally suited to driving short sheet piles, according to Sean McGee, sales representative for Mabey's Worcester, Mass., and Madison, Conn. offices.
The installation of the new pipe is being accomplished in a series of steps. First, Baltazar dug a 5-foot-deep "pilot-cut" trench along the entire length of the newer sewer right-of-way parallel to the existing interceptor. Next, the crew drove 25-foot-long XZ85 sheet piles on each side of the trench flush with the bottom of the pilot cut, which put the bottom of the sheet piling roughly 10 feet below the invert of the new pipe.
With the sheet piling in place, Baltazar's Cat 345 backfilled the pilot trench up to original grade, then the contractor began excavating and laying each section of PVC pipe.
In this phase, the contractor employed a steel trench box rented from American Shoring of Newburgh, NY during the removal of the backfill for each section. As excavation proceeded below the top of the sheet piles, the contractor lowered a heavy-duty framing system in place to brace the sheet piles. Rented from Mabey, this PowerBrace system consists of steel wales equipped with hydraulic rams and either mechanical or hydraulic transverse braces. Wales come in lengths up to 50 feet and are linkable. When employed in large rectangular or other multisided enclosures, the adjustable wales are also used as transverse braces.
For the Southington project, Baltazar employed long wales and 50-ton-capacity, JC40 mechanical bracing struts to support the pipe trench sheet piling, and four linked wales for the square manhole sections.
As work approached the section beneath the highway, soil conditions worsened, according to Zwicharowsky.
"Because of the presence of water and the nature of the soil, the engineers changed the method of installation, calling for completely encasing the pipe with concrete instead of using stone for bedding and backfill," he said.
For this 40-foot section, the contractor welded steel cleats to the sides of the permanent sheet piling and attached a 10-inch-deep rebar cage to the cleats. the pipe was positioned on top of the cage and then covered with concrete to a height of 3 feet above the pipe. This massive encasement and reinforcement slab is designed to prevent any movement of the pipe due to hydrostatic pressure from the high water table, said Zwicharowsky.
Once the installation of the new pipe is completed, Baltazar will install a Plug-It High-Flow Diverter in the manhole that is shared by the old and new pipe, to force the wastewater through the new sewer. Then crews intend to fill the old interceptor with grout and abandon it, completing the emergency project.