PND Offers Open Cell Sheet Pile System

With its ability to contain and encapsulate contaminated materials, prevent shoreside erosion and economically build bulkheads with wall heights no other method can achieve, PND Engineers Inc. hopes to expand the use of its Open Cell Sheet Pile (OCSP) System on the inland waterways.

While flat sheet piling has long been an industry standard, Bill Gunderson, PND’s retired principal, described the OCSP system as an interlocking, U-shaped configuration of flat sheet pile that can be formed into waste isolation bulkheads. Contaminated soil and debris are contained behind a series of interlocking sheet piles that are driven into the soil surrounding the waste, creating “isolation cells.” This can often be done more quickly and at a significant savings compared to conventional alternatives, Gunderson said.

The OCSP system can also be used for embankment stabilization using the arched face, vertical anchor walls working together to form a horizontally tied membrane that confines and strengthens the soil.

Open Cell technology has already been used in more than 250 applications since the 1986. It was designed and patented as a high-capacity bulkhead for berthing ships and barges as well as for shoreline erosion protection. OCSP structures have been built in some of the most extreme coastal environments, from the Arctic to the equator to the Middle East, and PND believes now is the right time to expand marketing efforts from blue water into brown water, especially at developable brownfield sites.

Previous activities at some of these sites left behind contaminated soils and debris that typically must be removed, treated or disposed of according to stringent environmental regulations before the sites can be repurposed.  Addressing these contaminants can often add significant costs to new projects, Gunderson said.

For waterfront facility owners, the burden of shoreline cleanup and restoration is often a prohibitive cost that prevents any beneficial redevelopment of the property, he said. Removal of old structures that are no longer functioning, repairable or required for current demands is simply too expensive. The ability to develop usable land and not have to remove materials that can be left in place is a logical approach that adds value, he said.

The Open Cell system is a proven technology to leave those items in place, safely encapsulating them and making the property usable again without prohibitive costs, Gunderson said. Using an OCSP bulkhead, the shoreline can be filled and the fill and debris retained inside the sheet pile wall so that the encapsulated fill creates valuable developable land over the original shoreline.

The installation of the OCSP typically results in minimal excavation or disturbance of the material behind the retaining wall, unlike other sheet pile wall systems, Gunderson said. The high tension in the face sheets forms a low permeability barrier to any material—liquid or solid—from moving from the fill-side into the waterway. Since OCSP systems can be economically built to wall heights over 60 feet tall, they work very well in the inland waterways where river elevations can seasonally fluctuate more than 40 feet, he said. In these cases, not only can the shoreline debris and contaminants be encapsulated, but new developable waterfront land can be created. A 60-foot wall height produces a 120- to 250-foot-wide strip of land behind the entire length of the bulkhead.

“Public and private entities, with facilities along the waterways, often inherit shorelines that have industrial debris and contaminants that need to be cleaned up,” Gunderson said. “The OCSP (system) has been used extensively for encapsulating both shoreline debris and leaching pollutants. The benefits are development of more usable land while eliminating the cost for removal and disposal of the debris and contaminants.”

Because one of the side benefits of the system is creating a nearly impermeable face, Gunderson said, it provides the opportunity for ports and businesses along the waterways “to use some very valuable waterfront space by not having to clean it up 100 percent,” Gunderson said. The Corps of Engineers tested and approved the OCSP system as appropriate for contaminated dredged material in 2009.

Encapsulating and containing brownfield sites is a newer use, PND senior engineer Carl McNabb said.

“We’re getting the message out that the technology is not only for reclaimed shoreline but also allows you to come in and do a restoration of shoreline,” he said.

The OCSP system has been successfully used to contain such contaminants as petroleum byproducts, burn waste with radioactive isotopes, creosote-treated piles and general (abandoned) debris, including a sunken warship in Iraq.

A recent inland waterway use for the Open Cell technology was building a bulkhead to support a crane at the Port of Owensboro (Ky.), McNabb said. Other uses for the technology have included the creation of a 300-foot-long Open Cell bulkhead to contain contaminated soils and encapsulate creosote-treated piles at a site for the American Construction Company in Tacoma, Wash., as well as building a 660-foot bulkhead built in two phases for a former oil refinery site in Kenai, Alaska, to stabilize eroding slope and prevent seepage of contaminants from the plant to the water.One major project involved isolating a landfill area at the former Alameda Naval Air Station in Alameda, Calif., adjacent to San Francisco Bay. The Environmental Protection Agency-designated Superfund site turned out to have a landfill that was significantly larger and deeper than originally thought. PND designed an Open Cell system with 48-foot wide cells creating a 12-foot high wall. The technology use resulted in a more than 60 percent savings in the project cost, PND reported.

Gunderson said the technology is proven, and the industry is already familiar with sheet piling, just not this adaptation for it.

“It’s use of sheet piling, which is an industry standard, in an unconventional way,” he said.

The company is available to discuss specific sites and create individualized concept white papers addressing any customer’s specific needs, including an initial plan and section view of an OCSP solution along with a rough order of magnitudes cost estimate.

Caption for photo: At left, a former pulp mill purchased by a pile-driving contractor in Tacoma, Wash., is in its original condition but with the Open Cell Sheet Pile System installed around it. The brownfield site was leaching contaminants and included treated piles and a submerged, treated timber bulkhead. At right, the same site after PND Engineers used the OCSP system to encapsulate the debris and control the leaching materials.  The OCSP bulkhead included a new berth developed for the contractor’s floating equipment. (Photo courtesy of PND Engineers Inc.)