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This Web Exclusive article was provided by Aaron Enterprises, an integrated provider of trenchless excavation technologies, including directional drilling, auger boring, pipe jacking, and micro tunneling as well as slip lining of existing pipelines. The company is located in York, PA.
Much of the discussion about aging infrastructure has to do with the decay of the dense web of underground water and wastewater pipelines that interlace the nation. Many of these are composed of corrugated steel that is designed to provide the pipes with structural strength that was intended to hold up for many years.
Unfortunately, those years have already elapsed for many of these underground pipelines. Decades of exposure to corrosion, rust, and erosion are now causing many of them to weaken and fail, causing problems such as cave-ins, flooding, and consequential damage that create emergency situations.
Depending on the type and location of pipeline, emergency open-trench reconstruction projects usually create challenging and seemingly interminable consequences, such as disruption of commerce, traffic detours, dangerous health conditions, and rebuilding of facilities.
Using trenchless pipe rehabilitation produces minimal disruption to surface areas and can be a less expensive and faster approach, not to mention providing better flow characteristics to existing piping.
To minimize surface disruption and avoid emergency situations such as pipeline cave-ins, it is recommended that regular pipeline inspections be done using video cameras or even walking personnel through larger pipelines in order to determine when and where repairs should be made. This should be done on an annual basis when pipelines have been installed 10 years or longer.
However, once a pipeline or portions of a water or wastewater pipeline require refurbishing, a savvy reconstruction method is the use of a trenchless technology known as “slip lining,” whereby heavy-duty, high-density polyethylene (HDPE) pipe is inserted through an original metal pipe system, providing years of extended service.
One of the most important benefits of trenchless pipe restoration, including the use of slip linings, is that it is minimally invasive. This means that the surface of areas where pipes are to be restored does not have to be excavated, which means less interference with traffic and businesses near the project site.
When compared to replacing with an entirely new pipe, slip lining is very effective and much lower in cost. While the slip lining must be of a lesser inside diameter than the “host” pipe, many times the flow capacity remains much the same because the new liner offers improved hydraulic characteristics.
“In cases where a portion of the original pipeline has caved in, we might have to shore up the collapsed area with a protective shield,” explains Vince Rice, president and CEO of Aaron Enterprises. “But for the most part, we simply dig a pit at a convenient position along the pipeline, and push the new liner through,”
Saving the day for shoppers
Rice says that slip lining is usually faster and more economical, and is an excellent solution when disruption of business or traffic is a key consideration.
Such was the case at The Point Shopping Center in Harrisburg, PA when an 800′ storm water drainpipe started to collapse beneath the center’s 25 acre, 1,200 car parking lot. Owned and operated by Cedar Realty Trust, Inc., what appeared to be a large sinkhole appeared in the lot during the summer of 2011.
“When I investigated the site, I found that the cave-in was not due to a geotechnical problem, it was the result of a failed drainage pipe caving in 30 feet under the parking lot,” says Robert Mastandrea, Cedar Realty corporate director of special operations.
Although he had no direct experience with slip lining at the time, Mastandrea had heard of it, and thought it might be a good solution for the situation at The Point. He explored the local market for a contractor with slip lining capability.
Instead of having to cut an 800′ open trench that would disrupt a large portion of the parking lot, which sometimes accommodates several thousand cars per day, a relatively small working pit (approximately 12′ x 40′) was dug at the far end of the lot, from which they slipped the liner into the drainage pipeline. The original 42″ diameter drainpipe was lined with a 32″ new HDPE insert.
“This approach saved us a lot of problems with business disruptions of the retail stores,” Mastandrea says. “That was very fortunate, since I am sure that the sight of a large open trench and heavy excavation equipment would have sent customers away from the center.”
When undergoing a project like this, facility managers will also want to conduct an evaluation of similar piping on other properties. This is the recommended approach for anyone wanting to ensure the quality and safety of their piping infrastructure. “That is normally the first step in a restoration program,” Rice says. “The evaluation allows us to establish priorities. It also enables us to recommend repairs that may be needed in the future, so that they can avoid emergency repair situations.”