The City of St. Cloud, Minnesota, had been periodically upgrading its wastewater system for many years, but intensity increased after a major failure near Halliday Road in 2008. The break prompted a review of the city’s entire sewer system and it revealed a severely deteriorating interceptor system.
During the ensuing inspections, the city learned that several areas were at high risk of failure and needed to be replaced. Much of the system had been constructed of reinforced concrete pipe (RCP) in the 1960s and 1970s, and had begun to exhibit severe hydrogen sulfide corrosion. The City of St. Cloud Public Utilities Department is responsible for 200 miles of sewer pipe in St. Cloud. The system also serves Sartell, St. Joseph and Waite Park. Located in central Minnesota, St. Cloud has a population of a little over 66,000. The City is a hub for post-secondary education, medical services and commercial access to the Mississippi River.
Results of the inspection indicated that more than 21,000 ft of sewer line needed immediate attention in order to prevent system failures and extend the useful life of the sewer interceptor system. With cost constraints in mind, the City divided the project into four phases. The first three phases of the $5.14 million dollar program started in 2009 and 2010 and were designed in-house by the City of St. Cloud Engineering Department specifying CIPP pipe.
Phase 1 replaced about 4,600 ft of sewer pipe from Halliday Road onto Roosevelt Road in 2009. Phase 2 replaced roughly 6,000 ft of sewer pipe along the Beaver Islands Trail south of St. Cloud State University in 2009. Phase 3 replaced about 1,900 ft of sewer pipe along Lancewood Drive in 2010. Phase 4 was to restore about 9,000 ft of the sewer interceptor system along Cooper Avenue and Roosevelt Road during 2013 and 2014.
Phase 4 was the longest section of the program, had the second largest diameter pipe and was located in the middle of the City’s commercial district. High traffic volumes downtown and on a major state highway and a busy county road necessitated minimizing surface disruption.
The City retained the engineering firm of TKDA, located in Saint Paul, to develop the preliminary design plan with a determination of the most feasible method of pipe rehabilitation.
“The City expressed interest in trying a method other than CIPP,” said Brad Hammerquist, TKDA engineer. TKDA’s proposal for the design of the project included discussions of sliplining as a viable alternative for portions of the project based on the long straight runs along Cooper Avenue and Roosevelt Road.
“The City had completed several sewer lining projects using direct replacement and/or CIPP,” explained Patrick Shea, Public Services Director for the City of St. Cloud. “This project was extremely sensitive due to the high traffic areas and alternate methods required the expertise and experience of a firm like TKDA.”
TKDA prepared a technical memorandum that provided an evaluation of sewer rehabilitation methodologies, including a comparison of cured-in-place pipe (CIPP) rehabilitation and sliplining with fiberglass pipe material. TKDA analyzed sewer tapes, documents, field notes, stakeholder’s lists, flow data, existing pipe characteristics, and preliminary construction cost estimates and made a recommendation to slipline with fiberglass pipe with a small segment of CIPP rehabilitation. TKDA took into consideration the extent of community disruption, bypass pumping, physical layout of the interceptor (straight runs and bends), cost and risk involved.
Sliplining, the majority of the project, would eliminate the need for a costly temporary bypass pumping system, and the excavation and replacement of streets. Sliplining is commonly performed under live flow conditions and allows for uninterrupted flow service.
Because of the long, straight segments on this route, the interceptor configuration was determined to be an ideal candidate for sliplining rehabilitation with fiberglass pipe, although a short section of CIPP rehabilitation along the route necessitated bypassing of sewage, according to Hammerquist. Few incoming sewer connections along the route would allow the contractor to push over 3,000 ft of fiberglass pipe. Only one intersection that involved a 90-degree turn and a bend would have to be repaired with roughly 500 ft of CIPP.
Bids from fiberglass pipe suppliers showed Hobas centrifugally cast fiberglass reinforced polymer mortar (CCFRPM) pipe to be the most economical choice. CCFRPM pipe has a high compressive strength, is relatively light weight, and has corrosion resistant properties. The fiberglass sliplining came to about 8,000 ft. It approximately included 5,000 ft of 54-in. pipe and 3,000 ft of 48-in. pipe.
Vince Paparozzi, Area Sales Manager for Hobas Pipe USA, coordinated closely with TKDA engineers throughout the design process to provide specifications, application information and costs.
The existing interceptor was believed to have sufficient capacity for future community growth. Although sliplining reduced the diameter compared to the existing RCP pipe, the inner surface of fiberglass pipe is incredibly smooth. The decreased friction of the fiberglass liner was much less than the friction associated with concrete walls. That was important because approximately 6 million gallons of wastewater per day flows through the sewer interceptor system below Cooper Avenue and Roosevelt Road.
Lametti & Sons Inc. of Hugo, Minnesota, was chosen to install the Phase 4 sliplining. Lametti has been a deep infrastructure contractor since the company’s inception in 1953. Over the years, it has become an expert at various methods of rehabilitation and it has considerable experience installing Hobas pipe.
Four access pit locations were identified to meet particular goals for the contractor. These goals included: minimize restoration, maximize length of lining runs, and provide sufficient space for staging and safe working conditions.
The existing 54-in. RCP pipe was sliplined with 48-in. Hobas along Cooper Avenue north from just north of 4th Street N (the location of Pit 1) to West St. Germain Street.
“At this point, we installed a reducer and lined 60-in. RCP with 54-in. Hobas to the corner of Roosevelt Road and University Drive South (Pit 2),” Mark Jay, project manager for Lametti, described the project. “We then installed 54-in. CIPP lining from this point for 1,100 ft to Pit 3 (due to the angle of the turn), and switched back to sliplining for a run of 2,894 lineal ft. The existing 60-in. RCP was out of alignment and Pit 4 was installed about 200 ft from the end of the last push. The remaining pipe was installed by hand.”
A Hitachi 750 hydraulic excavator crane with a Vacuworx Lifting System RC10 attachment was used to pick up the sections of pipe and lower them into a 30-ft deep access pit where an Akkerman SLS 50/100 ton slipline machine pushed the CCFRPM pipe into the existing line. A crew member safely operated the jacking machine by remote control to push the pipe into the old pipeline.
Lametti began the sliplining rehabilitation in October 2013 and completed the job in June 2014. Ordinarily, the project would have been completed in a much shorter time frame; however, the winter of 2013-14 proved to be the fourth coldest in Minnesota in recorded history. The extreme weather caused the work to be shut down on several occasions due to the danger of operating heavy equipment without the risk of major damage or compromising the safety of the crew.
“The use of Hobas pipe minimized disruption by alternate methods,” Shea said.
Recognized as being one of the most livable communities in the nation, the City of St. Cloud should experience reliable service from its rehabilitated Sewer Interceptor System for at least 75 years.
TKDA was awarded a 2014 Project of the Year Honorable Mention by the Minnesota Chapter of the American Public Works Association for its design of the St. Cloud Sewer Interceptor System Rehabilitation.