Case study - HB Construction Pipe Abandonment

Above: Low density cellular concrete being injected into the abandoned utility line.

Overview:

A 4-inch diameter by approximately 400-foot-long sewer line was being abandoned in Kansas City at an industrial site slated for new construction. It was specified by the engineer of record that the line had to be filled or excavated and removed to avoid future collapse which would result in settlement of soil. Concrete and utility lines ran parallel and directly above the line. Low density cellular concrete sprang to mind as an option.

Challenge:

The utility line was 4 feet underground and ran beneath a sidewalk, a roadway, and electrical utilities. The most straight forward solution would have included excavation and removal of electrical lines, then replacement of the existing concrete. This approach was not cost-effective, however, and would have meant disruption to vehicle and pedestrian traffic. The utility line was also too long to fill with a typical flowable fill or like material.

Low Density Cellular Concrete Solution:

Thrasher had a better, cost-effective solution. We provided the material specifications to the contractor and design engineer for approval to fill the line with Low-Density Cellular Concrete (LDCC). Cellular concrete is a process of introducing foam concentrate, water and air into a .5 water-cement ratio (slurry). One cubic yard of slurry yields 3.6 yards of LDCC at a wet cast weight of 30pcf (pounds per cubic foot) and compressive strength of 140psi. This method of pipe abandonment was approved and specified. Using LDCC, Thrasher was able to provide a solution that would only require one injection point and one relief point in the line in order to fill the 400-foot-long 4-inch line. A 30pcf cellular concrete material was injected into the utility line.

Above: Priming the line and weighing the cellular concrete. Material is injected into the utility, exiting the relief valve at the end of the utility.

Brett Haugland, the Civil Engineer of Continental Consulting Engineers had this to say,

"Removing the abandoned force main was a costly option, as it was installed beneath a sidewalk with other existing utilities in conflict. Finding a product that could flow a significant distance thru a small 4" diameter pipe was difficult until Thrasher introduced us to a product that met the requirements of the project and the City. Thrasher assisted the contractor during the implementation process and in the end, saved the project considerable cost as an alternative to removing the line."

LDCC can be used in many applications. It is a very stable and lightweight fill material that has compression strengths that exceed traditional backfill. LDCC can be produced to be a permeable or non-permeable material. It does not break down, expand or contract when cured. (See another Thrasher application of LDCC, here.) Due to the lightweight of cellular concrete, it can be pumped up to 10,000 feet utilizing one injection point. This makes LDCC the best option available for annular fills and pipe abandonment.

"They were able to utilize their expertise to adapt to an unusual situation and keep our project moving forward. Our other options would have cost us tens of thousands of dollars more!"

Results:

The team filled the line in less than 3 minutes and the total time on project was approximately 3 hours.

"Thrasher was recommended to us through an engineer working on our project. They were able to utilize their expertise to adapt to an unusual situation and keep our project moving forward. Our other options would have cost us tens of thousands of dollars more! Very satisfied with the results," said Jason Falldorf - Project Manager for HB Construction

"We never know how we can best help until we see the whole picture," said Kevin Lakey, Solutions Specialist & Project Lead. "Low density cellular concrete is a great solution for anyone who is facing an abandonment challenge. This would include projects where they have to address abandoned tanks, pipelines, sewers and other structures. We're here to help."

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