Gaining Ground: The Importance of Efficient and Effective Foundation Support

By Brendan FitzPatrick, P.E. | June 05, 2007
Ever since its inception in 1978, the U.S. ethanol industry has dedicated its efforts to increasing public awareness, developing investment opportunities and influencing public policy in order to make the fuel a front-runner in the ever growing pursuit of alternative fuel resources.

The Renewable Fuels Association reports the industry saw a dramatic increase in 2006, indicated by the record 4.9 billion gallons of ethanol produced, 15 biorefineries that came on line and 73 more under construction at the end of the year. Those are very impressive statistics for an industry that not only provides a renewable energy source, but also brings welcome economic revitalization to the areas where plants are located.

However, as the saying goes, to those whom much is given, much is expected. So it is with the ethanol industry. Its success, coupled with the ever increasing concern over global warming and general environmental preservation, has led to numerous legislative mandates, including those rolled out during President George W. Bush's State of the Union address in February. The pressure to construct new ethanol plants, while paying close attention to cost and timelines, has reached an unprecedented high. This pressure is driving many owners and general contractors toward more innovative building solutions.

It's important for the industry to begin taking note of how the very important first step in the building processproviding foundation supportcould be a means to that end.

From the Ground Up
The construction of ethanol and other biofuel facilities results in high applied foundation and tank bearing pressures, a particularly problematic combination in areas with inadequate soil stability. As plants continue to move outside of the Corn Belt into states like Arizona, Texas and New York, owners and general contractors must be able to find cost-effective and efficient methods to deal with less-than-ideal soil conditions.

In the past, solutions for soft or compressible soils were limited to only a few options. One method was overexcavation and replacement, which removes the unsuitable soil and replaces it with improved engineered material. This has proven to be a highly effective, though not particularly timely, method for foundation support. Time considerations are of particular importance when one considers the multiple components of an ethanol facility, including fermentation tanks and grain silos that may spread out over many acres. While the overexcavation and replacement method may adequately serve the initial plant's construction, stability issues can be encountered with ethanol plant additions/expansions, requiring temporary shoring and sheeting to prevent the movement of preexisting structures.

Deep foundations have also proven themselves reliable for foundation support. Deep foundations, such as driven and auger-cast piles or caissons, are used to bypass the poor soils and transfer loads to deeper bearing layers. Their utility is widespread, because they are designed to support very large design loads. Aside from cost, one potential drawback to their usage in ethanol facilities is that they have a slower installation process. Time must be allocated for the concrete piles to cure.

Introducing Another Alternative
It's said that necessity is the mother of invention. While acknowledging the usefulness of the overexcavation and replacement method and deep foundation system, but also recognizing their limitations in certain circumstances, owners and general contractors may want to consider the use of a trademarked Rammed Aggregate Pier (RAP) system, which provides a viable soil reinforcement alternative for ethanol production facilities.

RAP systems operate by utilizing lateral displacement methods and vertical ramming energy to strengthen the existing site soils. RAPs involve drilling a cavity to depths ranging from seven to 30 feet, allowing one to see the soil between borings and therefore prepare a unique design approach for each application. Layers of aggregate are introduced in thin lifts. Then a patented beveled tamper rams each layer, creating stiff RAP elements to support heavily-loaded foundations, tanks, process areas and ancillary structures.

One recent application is that of E3 BioFuels, in a groundbreaking 24 MMgy ethanol production facility powered by cattle manure in Mead, Neb. It's the first facility of its kind to begin operation in the United States. To keep construction costs down, Katzen International Inc. was tasked with evaluating foundation strategies for the facility's massive fermentation tanks, beer well tank, digester tanks, grain silo and utility corridor. Thiele Geotech Inc. conducted the geotechnical exploration and found a soil profile with 15 to 20 feet of soft-to-medium-stiff loessial clay over medium-dense-to-dense sand, creating less than ideal conditions for such heavy loads.

Deep foundations can hold serious cost and availability concerns. There are also potential seasonal construction challenges that inhibit overexcavation and replacement. Therefore, Katzen had Thiele evaluated RAP system. After evaluating the design approach and standards, the RAP system was chosen because the finished product was easier to maintain and its installation process fit the project's expedited construction timeframe. RAPs often allow for foundation subcontractors to begin work on-site, even while the installation process is taking place nearby, resulting in a significant source of time savings and an asset for ethanol facilities under strict time constraints.

Gaining Ground
The ethanol industry has expanded significantly beyond the Corn Belt and continues to grow into areas around the United States and the globe. As the industry continues growing, finding and integrating effective and time-saving methods in the construction of new and expanding ethanol production facilities will become more imperative.

Owners and contractors are going to continue to face situations where subsurface soil conditions are inadequate to bear the load created by massive ethanol facilities. Thus, effective and efficient methods for reinforcing the soil are going to continue to be a first line of defense for those owners and contractors. While traditional overexcavation and replacement and deep foundations are well known in the engineering world and certainly have their place in ground improvement, RAP systems provide a viable alternative for soil reinforcement and provide for expedited timelines in the fast-paced growth of the ethanol industry. Just as the ethanol industry is revolutionizing the alternative fuel industry, it is vital that the geotechnical community continue to revolutionize the way it provides foundation support for the industry's varied applications.

Brendan FitzPatrick, P.E., is the director of engineering/development-North America for Geopier Foundation Co. Inc., headquartered in Mooresville, N.C. Reach him at (800) 371-7470 or bfitzpatrick@geopier.com.

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