Battling the Aging Pipeline Infrastructure Through Sliplining

Much of the discussion about our 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, expensive emergency open-trench reconstruction projects usually create nasty and seemingly interminable consequences, such as disruption of commerce, traffic detours, dangerous health conditions and extensive 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, the savvy reconstruction method is the use of a trenchless technology known as sliplining, whereby heavy-duty, pipe is inserted through an original metal pipe system, providing many years of extended service.

One of the most important benefits of trenchless pipe restoration, including the use of sliplining, 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 much less interference with traffic and businesses near the project site.

When compared to replacing with an entirely new pipe, sliplining is very effective and much lower in cost. While the sliplining 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, you might have to shore up the collapsed area with a protective shield.  But for the most part, you can simply dig a pit at a convenient position along the pipeline, and push the new liner through.

Saving the Day for Shoppers

Sliplining 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-ft 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., a fully integrated real estate investment trust that owns more than 90 shopping centers nationwide, 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 ft under the parking lot,” says Robert Mastandrea, Cedar Realty corporate director of special operations.

Although he had no direct experience with sliplining 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 sliplining capability and decided to contact Aaron Enterprises.

“Aaron engineers visited the site, evaluated the situation and then recommended the slip liner approach,” Mastandrea explains. “So, it looked like we had the right technology. The firm was also equipped to shore up the cave-in and could handle the re-paving requirements, so we had a single bid opportunity.”

Instead of having to cut an 800-ft open trench that would disrupt a large portion of the parking lot, which sometimes accommodates several thousand cars per day, Aaron dug a relatively small working pit (approximately 12 ft by 40 ft) at the far end of the lot, from which the crew slipped the liner into the drainage pipeline. The original 42-in. diameter drainpipe was lined with a 32-in. 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.”

The Quarry Quandary

Another storm water pipeline collapse occurred a year ago at a major quarry located in Virginia. The pipeline, which is approximately 800 ft long, is part of a storm water diversion system that protected the quarry and surrounding area from flooding that could result from heavy weather.

Under normal circumstances, the diversion pipeline drained into a nearby river. However, when a hurricane struck the region, the aging 72-in. pipeline, buried under 75 ft of earth, partially collapsed and threatened to flood the quarry as well as a nearby asphalt plant.

Engineers from Aaron Enterprises were called in to survey the situation, locate the section where the collapse had occurred, and recommend a solution that would prevent future flooding and collapses.

Aaron Enterprises found a way, using a tunneling shield and a new steel casing, to do an encapsulation and removal of the collapsed pipeline. Crews had to tunnel back 150 ft and remove large boulders, tree stumps and the collapsed corrugated pipe from the discharge end. An 800-ft length of 63-in. HDPE liner, weighing 208,000 lbs was then fused together and pulled through the existing and newly encased portion of the corrugated pipe. The annular space between the host pipe and the new HDPE liner was then pressure grouted to restore the overall structural integrity to the pipeline.

To avoid other catastrophic problems, the quarry owner asked the Aaron Enterprises’ team 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. The evaluation allows Aaron to establish priorities. It also enables them to recommend repairs that may be needed in the future, so that emergency repair situations can be avoided.

Vincent T. Rice is president of Aaron Enterprises Inc., an integrated provider of trenchless excavation technologies, including directional drilling, auger boring, pipe jacking and microtunneling, as well as sliplining of existing pipelines.
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