CCCP Only Viable Solution for Urgent Culvert Rehabilitation
In February 2018, a multi-day storm event led to overfilling of an underground culvert in Madison, West Virginia, which in turn caused a massive sinkhole in the Kroger parking lot, a sinkhole big enough to endanger cars and shut down access to the supermarket for days.
That was a big deal; Kroger is the United States’ largest supermarket chain by revenue, and second only to Walmart as the largest retailer of any kind. The company brings the resources of a large city to asset maintenance and restoring access to the Madison store was an urgent priority.
Senior project manager John Ball of Goal Technical LLC got the call from Kroger, alerting his company to the problem. But determining the cause of the sinkhole was difficult, given the location and circumstances. The culvert passes under 650 ft of the Kroger parking lot, confined to an 84-in. — 7-ft — diameter corrugated metal pipe (CMP) culvert for the entire length. The upstream 500 ft of culvert is about 10 ft below pavement, and the downstream 150 ft is about 17 ft below pavement — the grade change is accomplished by a 30-degree downward bend, a little like an underground waterfall.
As a stopgap, Goal Technical pumped concrete grout into voids around the sinkholes and managed to stabilize the parking lot. Meanwhile, Ball began looking for a more permanent solution to what proved to be a recurring major problem — sinkholes reopened in March and May of 2019.
“We explored options, did more exploratory work, and came up with a plan for a permanent fix,” says Ball. “Eventually we settled on centrifugally cast concrete pipe (CCCP), and CentriPipe in particular, for the entire 650 ft of CMP culvert.”
Multiple Repair Challenges
Exploratory work at dryer times of the year soon revealed that rotting CMP inverts along most of the culvert, especially in the area of the grade change — inverts were completely gone, and pipe walls were also severely damaged — led to scouring and large voids, and then to sinkholes, which occurred near the bottom of the 30-degree grade change.
“Apparently, the water velocity at the area of the downward bend was so great that it ate away and eroded the pipe,” says Ball. “In places, the CMP inverts were completely gone, along with patches of the rest of the culvert.”
So now Goal Technical knew what needed fixing… but how to fix it was still a mystery. Several major challenges presented themselves:
The rehabilitation solution had to be completely structural (independent of the CMP substrate) and smooth-walled, and not simply a CMP patch or a void-stabilization strategy (which had already failed).
Flow capacity of the 84-in. CMP culvert needed to be preserved to avoid flooding.
Kroger ruled out trench-and-replace early in the design phase — given the depth and size of the required trench, the work would have been prohibitively expensive and disruptive to store operations.
Cured-in-place pipe (CIPP) was ruled out early, mainly because a mid-culvert grade change with two 30-degree bends is an extremely difficult configuration to address seamlessly (or without wrinkles) with CIPP — and any seams or joints or weak spots in this area would be vulnerable to the same forces that destroyed the original culvert.
The same factors that ruled out CIPP, and the need to preserve flow capacity, also worked against sliplining, spiral wound pipe and several other common trenchless solutions.
“Eventually we settled on CentriPipe as the right way to rehabilitate the Hopkins Branch culvert,” says Ball. “It met all our conditions, and really was the only thing that would work here.” Scott Benner, owner and eventual CentriPipe subcontractor Centrifugal Lining Inc., agrees. Centrifugal Lining also does CIPP sewer rehabilitations, a technology Benner believes in, but he says that “CIPP just would wouldn’t work here and wouldn’t be cost-effective. But CentriPipe was just perfect. Even so, this is one of the more difficult and interesting sewer repairs we’ve ever been involved in.”
A Trenchless Solution
CentriPipe is a CCCP solution, developed by APM LLC, that relies on a concrete SpinCaster pulled through sewers and high-strength fine aggregate composite concretes (FACC) specifically designed for sewer applications. The SpinCaster is inserted into failing sewers and withdrawn at precisely-controlled speeds while casting a new concrete pipe within the old pipe. What makes this simple technology so effective is the detailed application principles developed more than 20-plus years of use in large and small sewer rehabilitations. Details that improved the quality of the Kroger project include:
The newly cast PL-8000 pipe adhered tightly (leaving no annular space) to the original CMP and was quite thin, just an inch over the culvert corrugations. This thickness was more than enough for adequate strength, while also being thin enough to minimally affect culvert volume.
Bends and grade changes in sewers can typically be cast seamlessly, leaving no weak spots in the area of the grade change.
Because the FACCs used in the CentriPipe process cure quickly and can be used in moist conditions, CentriPipe projects are usually accomplished quickly. The Madison, West Viriginia Kroger, total onsite project time was just three weeks, and store operations were never disrupted.
Aside from the grade change described above, this project presented no special difficulties. After dewatering, the entire length of failing invert was rebuilt with APM, LLC FACC PL-12,000, and some CMP sections were patched with sprayed PL-12,000. Then, several CentriPipe runs of about 200 ft were completed in less than two weeks, working from access points at both ends and a mid-culvert access manhole. And… that was it; a durable, trenchless, high-quality restoration of a badly failing CMP creek diversion was completed in three weeks with no disruption to surface activities and no return of sinkholes in the following wet season.
Angus Stocking is a former licensed land surveyor who has been writing about infrastructure since 2002.