Civil Engineering

The Latest Dirt on Soil Compaction

5 Jun, 2007 By: Andrew G. Roe,P.E.

Intelligent technology has landed and is gaining ground in heavy equipment operations.


Few people use the words “intelligence” and “dirt” in the same sentence, but that may change if some emerging technology gains a foothold in the construction industry. The use of IC (intelligent compaction) equipment, which allows construction crews to monitor in real time the compaction of roadbeds and other earthwork projects, offers new ways to improve pavement durability and construction efficiency.

Although the technology has been used in Europe for several years, IC has only recently gained momentum in the United States as research progresses and test projects provide data demonstrating its reliability. Early indications are that IC can deliver numerous benefits to owners and builders, although challenges remain in areas such as data management and standardization of IC practic es.

How It Works
Definitions of IC vary, but in general, the technology measures soil compaction parameters by equipping compaction equipment with sensors that monitor soil compaction, and global positioning systems that locate where readings are taken. Vibratory rollers are equipped with accelerometers that measure either displacement of the rolling drum or acceleration forces exerted by the drum, providing data that can be correlated into soil compaction values. By recording data in real time and using GPS equipment to record location data, soil compaction data can be mapped to identify problem areas and guide equipment operators to where more compaction is needed. Some equipment can even adjust compaction energy as readings are received.

Intelligent compaction equipment uses accelerometers within the drums and GPS systems to monitor location. (Figure courtesy of Caterpillar.)

Because the durability of roadways, parking lots and other projects relies heavily on proper compaction of subgrade materials, IC could have wide-reaching benefits. The capability of monitoring compaction throughout an entire grading project, rather than spot checking with individual field tests, could revolutionize practices for verifying quality of roadway and site grading.

“Quality control in the past was centered on field tests and inspection,” said David White, assistant professor of civil, construction and environmental engineering at Iowa State University. With the spot checking approach, “you really don’t end up testing much” of a project site. “Now you can have virtually 100% coverage,” he said. White has been researching intelligent compaction of soils and asphalt under funding from the Iowa Department of Transportation, Minnesota Department of Transportation and the Federal Highway Administration. MnDOT has used IC on several highway projects since 2005 and stated in a recent report that IC rollers "exhibited tremendous promise for use as QC tools on project sites.”

Hurdles
Although research by White and others has yielded encouraging results, several hurdles remain before IC can be widely adopted in the standards-driven U.S. construction industry. With different manufacturers offering various IC techniques and equipment, state DOTs and other public agencies need to develop standard specifications before IC can be used routinely on roadway projects. Additional equipment costs could also hinder widespread adoption. According to a 2006 Construction Equipment report, IC systems can add up to 30% to the cost of conventional compaction equipment.

“No contractor is going to buy this until it’s specified,” said Jon Sjoblad, senior marketing communications specialist at Caterpillar in Champlin, Minnesota. Caterpillar is one of several manufacturers offering IC equipment, along with Ammann, Bomag, Dynapac, Ingersoll-Rand and Sakai.

Managing the massive amounts of data is also a challenge, said White. His research has used ArcView from ESRI to manage data in a GIS environment, with special computer algorithms developed for postprocessing data. On-board systems such as Caterpillar’s Accugrade system can be used to integrate compaction data and CAD data to graphically display information to operators in real time. The onboard systems expand on the machine control technology used to guide earth-moving equipment (see " GPS-Guided Earthmoving Gains Ground," GIS Tech News, January 2, 2007).

Underground voids can be detected with IC equipment. (Figure courtesy of Caterpillar.)


Onboard displays provide operators with real-time compaction information. (Figure courtesy of Caterpillar.)

IC also offers other benefits, such as identifying underground pipes, voids and soft materials. “It’s an emerging technology. All the benefits may not have fully arisen yet,” said Sjoblad.

Construction efficiency and site safety can also be improved with IC, as testing operations are consolidated with construction. Conventional compaction tests are often conducted in the vicinity of operating equipment, potentially disrupting operations and putting field personnel at risk. With IC, “the contractor is in better control of operations,” said White.

Even with all the potential benefits, users should not expect IC to solve all their compaction problems, cautioned Sjoblad. “It’s not a miracle worker. It can give you an indication that something is wrong, but you have to understand what’s going on” to properly apply IC, he said.


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