Cutbacks involve too much labor

New soil compaction meter solves some common problems in the utility industry

Bill Wilson / December 28, 2000

When it comes to soil compaction testing, Memphis Light Gas and Water (MLG&W) found a solution in the real-time feedback provid

When it comes to soil compaction testing, Memphis Light Gas and Water (MLG&W) found a solution in the real-time feedback provided by the Soil Compaction Supervisor developed under the sponsorship of GRI (formerly Gas Research Institute).

Serving the city of Memphis and Shelby County, MLG&W is the nation’s largest three-service municipal utility. For over 60 years, MLG&W has been a customer-focused company dedicated to providing quality service at the lowest possible rates. The publicly-owned company has been vigilant in exploring several advanced technologies, including the Soil Compaction Meter.

"Soil compaction is a hot issue in the utility industry," said Gene Crawford, MLG&W’s assistant manager of distribution support. "Any technology that enables our crews to verify proper compaction on the initial dig can be a major cost saver, both to us and the city of Memphis, because it eliminates claims, customer complaints, callbacks and cutbacks."

Cutbacks, Crawford explained, involve cutting a 6- to 12-in. lip around an excavated hole after soil reinstatement. The lip supports overlays of concrete and asphalt. "If you can verify and document that proper compaction density has been reached and that the reinstated hole is structurally sound, you don’t need the extra support of the cutback, which is a very labor-intensive process. Our ability to verify and document that proper compaction has been achieved, combined with our ability to eliminate cutbacks, will save MLG&W and the city of Memphis significant dollars," said Crawford.

Zero failure

Meeting stringent soil compaction requirements for utilities across the U.S. was the goal GRI had in mind when it developed the Soil Compaction Supervisor (SCS).

The new technology is seismic in nature and operates on the principle that progressively denser soil transmits pressure waves with progressively greater efficiency. While the technology embodies sophisticated software and mathematics, in layman’s terms, the soil compaction technology monitors a decreasing rate of increase in pressure wave amplitude and gives the stop compaction signal when it is determined that continued compaction activity is not resulting in further meaningful increases in pressure wave amplitude.

The hand-held, battery-operated meter receives input from a disposable piezoelectric sensor that is placed at the bottom of an excavation before compaction begins. The sensor is connected to the meter by a plug-in cable. The meter is self-adjusting to allow for different soil types and establishes a fresh "maximum soil density" calculation for every lift of soil. When maximum compaction is reached, the meter’s signal light changes from green to red. All pertinent data during soil compaction are stored.

Initially, MLG&W demonstrated the SCS for the Division of Engineering, Construction and Inspection Department of Memphis in a small pilot area of town where compaction sites would be monitored with the new technology. "We expect zero failure on these Soil Compaction Meter sites," said Crawford.

The results will assist MLG&W and the city to work together on issues such as cutbacks, one-step pavements and use of steel plates during gas main repairs. MLG&W has purchased 12 Soil Compaction Supervisors that will allow MLG&W and the city to confirm and document performance of the soil compaction process.

Dr. Kiran Kothari, GRI principal project manager, distribution automation and operations, stated that the industry is pleased with initial results of the soil compaction meters.

"The gas industry was looking for a more practical means of verifying soil compaction quality," he said. "GRI’s developmental goals called for a technology that was low cost, could be easily used by field personnel, was fast and could provide reliable information.

"The seismic approach enabled us to satisfy our developmental goals and provided an opportunity to apply the technology in real time. The real-time aspect of the technology not only provides for compaction verification, it does so in a fashion that eliminates guesswork. The meter tells the compactor operator when he has reached optimal compaction and can stop compacting."

Kothari indicated that the final product, the Soil Compaction Supervisor, allows the meter operator to record job specific information, such as site number or location, time, date, number of lifts, compaction time per lift, total work time and type of compactor used on the lift. Pertinent information on the job and compaction activity is stored in the SCS. The data can then be downloaded to a computer for additional analysis and archiving. The Soil Compaction Meter and Soil Compaction Supervisor have been independently tested at various sites.


Information for this article provided by Double D Associates, Butler, Wis.

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