October 2012, Vol. 67 No. 10
Features
Pre-Chlorinated Bursting: Cost Effectiveness On A Large Scale
The Charter Township of Brownstown, MI, has undertaken an ambitious water-system improvement program that includes installing nearly eight miles of new water mains. Most of the project involves installation of pre-chlorinated HDPE pipe by the trenchless pipe bursting process.
Construction is occurring at various locations throughout the Township. Much of the construction in the southern end of the township is in an area of one-time cottage communities that have become full-time residences in this pleasant community of 30,000, some 20 miles south of Detroit. Pipes also are being replaced in older subdivisions where deteriorated mains are susceptible to breaks.
Older areas of the Township have experienced interruptions of service caused by breaks and increased capacity is needed in areas that have experienced significant growth with increased water demands.
Township Public Works Director Mark Gahry said the project is Brownstown’s first experience with pipe bursting and the use of pre-chlorinated pipe. “The Township is very progressive,” Gahry said. “I have kept abreast of developments in technology and the various trenchless construction methods appropriate for the Township’s needs. I have been on pipe bursting projects and the contractor conducted an impressive demonstration that really sold me on the technology for our water main improvements.”
Gahry said the use of pre-chlorinated pipe is not common in Michigan, but he has been on projects where it is used and investigated it thoroughly before committing. “I wanted to be sure we understood what we were getting into,” he added. “It is a recognized and accepted process and the Environmental Protection Agency now has guidelines for it.”
Proponents say that pre-chlorination of pipe prior to installation by pipe bursting allows the existing system to remain in use, reducing system downtime and eliminating post-construction testing.
Joint venture contract
The Brownstown water improvement project is a joint venture of Bidigare Contractors Inc., Northville, MI, and D & D Water & Sewer, Inc., Canton, MI. Their contract calls for installation of 43,000 feet of new water mains, most of it 8- and 12-inch pre-chlorinated HDPE pipe. The contract also calls for installation of fire hydrants and gatewells.
Because construction is taking place in mature neighborhoods, trenchless methods of construction are being used to limit surface damage and disruption of traffic and routine activities, said John Bidigare, vice president of Bidigare Contractors. Most, he said, is by pipe bursting, with some segments installed by horizontal directional drilling (HDD).
The pipe bursting process uses a bursting tool which is inserted into the pipe being replaced. The tool is pulled through the old pipe, shattering or splitting it. An expander behind the head displaces fragments or pieces of pipe as new pipe is pulled in behind it. Two types of bursting tools are available: a pneumatic bursting head uses percussive action to crack pipe; static heads are equipped with blades that cut or split the pipe.
Key benefits of the method are reduced excavation requirements allowing new pipe to be installed in urban areas where restoration would be costly and disruptive and the ability to increase the size of new pipe. Bidigare said that in Brownstown, approximately 115 bursts will be made with average lengths of 375 feet. Average depth of the host pipe is six to 7 feet at the invert. In residential areas, service connections were reinstated immediately after each burst was completed. Because of the relatively short lengths of the bursts, water customers were without water for only a few hours the day of construction.
“Pipe bursting was chosen for the Brownstown project to increase the size of the existing main in the location of the old main for several reasons,” explained Bidigare. “One is to minimize the surface disruption caused by excavation and the restoration it requires. The Township is an advocate of trenchless technology, and Wayne County has adopted a new policy that abandoned pipe be removed from the ground and not abandoned in place which would have caused increases in the project cost and the schedule to complete the work.”
Bidigare said most construction is in Wayne County Road right-of-way which has grass/landscaped surfaces with some paved areas. Subsurface conditions are in fill material of previous trenches above the existing water main. The old pipe was assessed from record drawings, previous repair experience and other factors. Locations of pipes are confirmed by opening and inspecting gatewells.
The plan
A burst plan was developed and reviewed with the project engineer and client. The plan identified the length of each burst, the number of gatewells, hydrants and services along the burst paths, and any other water main connections required.
Based on this information a reasonable burst length was determined, based on what could be completed in a normal work day and services reinstated at the end of the day. The preferred locations to access the existing pipe with the bursting tool are fire hydrants or gatewells with an exit pit serving as the entry pit for the next burst.
On the project, a typical burst will start at around 9 or 10 a.m. and be completed around 1 to 2 p.m. That leaves three to four hours for hydrants, gatewells and service installation. There has been sufficient space in neighborhoods to assemble pre-chlorinated pipe runs in accordance with EPA guidelines. Pipe is fabricated at nearby right-of-way areas that do not impact residents driveways and moved into place on burst day. Residents along the burst path typically are without water for one day from 8 a.m. to 4 p.m.
The equipment used to make the bursts is a HammerHead HydroBurst HB80 static pipe bursting system. The HB80 is powered by a 72-horsepower diesel engine that drives a 31 gpm variable displacement hydraulic pump developing 80 tons of pulling force. Available with an optional automatic rod spinner providing 16-second payout of 35 inch-long lengths of lightweight, heat-treated rod that is flexible enough to negotiate bends in the host pipe. Rod storage capacity is 148 feet. API-style joints effectively accommodate thrust loads encountered when pushing around sweeping bends and encrusted or collapsed pipes. A standard feature on Hammerhead static-bursting equipment is a rod-lock device that places constant tension on pipe string, eliminating rod rebound and increasing production. Optional hydraulic leveling and jacks adjust to place the machine on grade and aligned with the existing pipe. Adjustments can be made during the burst as conditions change without stopping the bursting process.
Early stages
The installation by pipe bursting of pre-chlorinated HDPE water pipe — pipe that is disinfected before placement in the ground — is widely used in Europe, but is in its infancy in the United States.
“In this method, the pipe string to be installed is fabricated above ground,” explained Mark DiMichele, P.E., president of D & D Water and Sewer. “The assembled pipe is pressure tested, chlorinated and tested for bacteria by a state-certified lab.”
Once the pipe has been approved for use, it remains sealed until installation day. “It can remain in this condition for a maximum of 14 days,” DiMichele continued. “On burst day, the replacement pipe is drained, the pulling head is fused on and burst into place. Upon completion of the burst, all water services, gatewells, fire hydrants and other connections are completed.
“After completing all connections, a ‘pig’ is flushed through the newly-installed water main, along with a slug of chlorine. After the ‘pig’ exits the pipe, a flushing cap is installed and allowed to flush from the existing water system for approximately two hours. A final sample of the water from the new pipe is taken for lab testing. The reconnected water services are opened and allowed to flush. As a precaution, the residents are given a two-day boil water notice until confirmation is received from the testing lab. “Utilizing this method of construction, the water customer only sees significant construction activity in front of their home for one day.”
By late summer, pipe bursting for the Brownstown project was approximately 70 percent complete with work projected to be finished in the fall of 2012.
Is the Township satisfied with the pipe bursting process and installation of pre-chlorinated pipe? “Absolutely,” said Public Works Director Gahry. “In fact, plans are to expand the project to include another 30,000 feet of mains which would extend the completion date to 2013.”
Bidigare Contractors has been active in Southeast Michigan for over 20 years, providing municipalities, developers and builders with underground construction services, site development, demolition, bioswale and rain garden construction and general contracting.
D & D Water & Sewer, Inc. was established in 1970 and specializes in water service installations, water main repairs and provides those services to several Michigan communities, including Brownstown, Van Buren Township, City of Novi and Woodhaven. D & D has been providing pre-chlorinated water main pipe bursting and sanitary sewer pipe bursting since 2007.
Manufactured in the United States, Hammerhead offers a wide range of pipe bursting equipment to replace fracturable and non fracturable pipe ranging from two through 36-inches. In addition to pipe bursting systems, the Hammerhead line includes pneumatic piercing tools, pipe ramming equipment, HDD assist and downhole tools.
FOR MORE INFO:
Bidigare Contractors Inc., 248-735-1113, http://bidigarecontractors.com/
D & D Water & Sewer, Inc., (734) 397-3386
Hammerhead (Earth Tool Corp.), (800) 331-6653, www.hammerheadmole.com
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