January 2013 » Features

Riverfront erosion protection
Losing 18 inches of riverfront to erosion each year was threatening the stability of walls protecting the city of Sunbury, Pa., from frequent flooding of the Susquehanna River. So in late 2010, the city began a major revitalization project to repair its damaged riverfront. Building walls to protect the riverbank in Sunbury dates back to the 1930s, when the Works Progress Administration (WPA) constructed a natural stone wall along the riverfront to stabilize the banks of the Susquehanna. An additional flood wall was added above the WPA wall in 1951 by the U.S. Army Corps of Engineers.

However, the site was in need of serious repairs. Plans for the renovation began taking shape in 2000, and included stabilizing the riverbank plus adding a pedestrian walkway that would start in the downtown area and cross over the floodwall to lead to the Riverfront area complete with amphitheater, walking paths, and a marina. To make this happen though, the city first needed to stabilize the river bank.

The city of Sunbury had already begun the first phase of the renovation when Jason Metzger, project manager for the contractor, HRI Inc., suggested Redi-Rock as an efficient alternative to the walls that were planned – which included poured-in-place walls and restacking the WPA stone in some areas. HRI believed that Redi-Rock could save on installation time compared with restacking the original stone and match the look of the stone even better than the poured-in-place walls.

Jim California, P.E., lead structural engineer on this project from Buchart Horn Inc., and Scott Russell, P.E., regional manager of Buchart Horn Inc., agreed. "Redi Rock provided a robust retaining wall capable of sustaining periodic impacts by floating debris during periods of high river levels," they said. "In addition, the walls had the ability to maintain a more vertical profile, limiting the impact on the cross sectional floodway. In one location, there was an existing concrete wall in place that had experienced some apparent shifting. We wanted to leave the old wall in place and build a new structural wall in front of it. In this situation, geogrid tie-backs could not be used. The Redi-Rock system with its massive blocks and gravity wall capabilities worked well in this application without requiring geogrid."

To construct these walls, engineers designed one course of 60-inch base blocks in the base of the walls, with all 41-inch blocks above, except for 28-inch-blocks in the top course. The largest wall on the project lies in the river and is 485 feet long and 13.5 feet tall. To install this wall, contractors used a coffer dam to temporarily redirect the flow of the river.

Provisions were incorporated into the design to anchor a floating marina dock. Local Redi-Rock manufacturer Paxton Precast custom cast pipe for the dock attachment hardware, which connects directly to the Redi-Rock blocks. HRI supplied light fixtures that Paxton Precast also custom cast into the block along with pipe to run the wires through.

To match the retaining wall blocks' color to the original WPA walls, Paxton Precast visited the site multiple times to formulate a color scheme. Paxton used integral color as well as a shake-on color to help each part of the Ledgestone block faces stand out.

"Three floods have gone through the Sunbury area since we started excavating. One of the floods went through before we could complete one of the walls on the upriver side. After the flood, you actually couldn't even tell that there had been a flood. There was no damage at all," said Lenny Stopper, project supervisor for HRI.

The walls were installed during the summer of 2011 prior to a flood from Hurricane Irene in the fall. The walls were completely underwater but experienced no damage.

The walls were able to make it through the floods unscathed because of the engineering behind them. A concrete leveling pad was used in areas susceptible to more frequent high-water events, Russell and California said. Free-draining coarse aggregate was placed behind the wall to help deal with drawdown of water pressure behind the wall resulting from receding high water.

The knob and groove design of the blocks automatically aligns walls at the correct batter as blocks are stacked. The one-ton blocks can be used to build gravity walls without geogrid reinforcement.

Information provided by Redi-Rock International

Provisions were incorporated into the retaining wall design to anchor a floating marina dock.
The riverfront retaining walls survived more than one flood intact before installation was complete.

New roadway, drainage, and wetland improvements
The New York City Department of Environmental Protection and the New York City Department of Transportation broke ground on Oct. 16, 2012, on an upgrade to the water and sewer infrastructure of the Springfield Gardens section of Queens, N.Y. This is the fourth phase (Phase D) of a $175 million neighborhood infrastructure improvement project, designed by Dewberry, to solve chronic flooding in the community.

The $53 million phase involves 2.8 miles of new sewer line and 84 new catch basins. Approximately 3.5 acres of new wetlands will be created. Dewberry's design includes the following Best Management Practice wetland designs:

  • Springfield Lake will be dredged of 17,000 cubic yards of sediments to increase its depth and reduce algal blooms.
  • Stormwater from new storm sewer lines will be filtered in marshes and wetlands, helping to improve the water quality of Jamaica Bay.
  • More than 25,000 square feet of porous concrete will be installed in the median of Springfield Boulevard, allowing stormwater to pass through the concrete and be absorbed into the ground naturally. Stormwater will then be used by trees and other vegetation.

The Springfield Gardens sewer and water infrastructure upgrade is expected to be completed in 2014.

Information provided by Dewberry

LiDAR used to locate heat loss
Aging infrastructure and historic structures presented challenges at the Francis E. Warren Air Force Base (F.E. Warren AFB) in Cheyenne, Wyo., as the base desired to meet energy-reduction guidelines and work toward a "Net Zero" goal. F.E. Warren AFB sought Merrick & Company to perform LiDAR and thermal imagery services that would locate areas of heat loss from historic facilities on base.

With many historic structures dating back to the mid 1800s, F.E. Warren AFB needed to find a cost-effective approach to identifying where high heat losses were occurring, which they believed were from aging building roofs or in the high temperature hot water (HTHW) distribution system. The HTHW system heats most of the base facilities through a series of underground utility corridors, which are two to three feet deep concrete trenches with three-inch concrete caps, often overlaid with parking lots, roads, and sidewalks.

To analyze the existing base conditions, Merrick used a multi-sensor suite of the latest geospatial, remote sensing, and mapping technologies. Combined color digital aerial photography coupled with LiDAR, thermal imagery, and a variety of orientation technologies were integrated for best results.

Color digital aerial photography (left) coupled with LiDAR, thermal imagery (right), and a variety of orientation technologies were integrated to identify where high heat losses

By employing a thermal sensor with LiDAR in an airborne platform, rapid collection and analysis provided F.E. Warren AFB the exact location, extent, and temperature signature of the problem areas. The aerial technique using a Cessna 402B aircraft allowed hundreds of buildings (base wide) to be inventoried more cost effectively. The underground HTHW system was easily detected using these technologies, which otherwise would have been impossible because of the several inches of concrete and paving overlays onsite.

Merrick's findings will allow F.E. Warren AFB to initiate a base-wide assessment and maintenance plan for all of the buildings and underground HTHW piping on a consistent baseline.

Information provided by Merrick

Wastewater management facility improvements
Preserving the water quality of Orange County's beaches is of great concern to the citizens of Southern California, and the mission of the Orange County Sanitation District (OCSD) is to do everything in its power to prevent wastewater from contaminating the county's 42 miles of Pacific coastline. To support that objective, OCSD selected Atkins to provide the engineering, inspection, condition assessment, and construction-document preparation services the district needs to engage in a series of key improvements to its wastewater management infrastructure.

OCSD is tasked with the safe and environmentally sound collection, treatment, and disposal of the 210 million gallons of wastewater generated each day by more than 2.5 million people who live in a 479-square-mile area of central and northwest Orange County.

According to Atkins Project Director Cenk Yavas, OCSD will be constructing a new Final Effluent Sampler Building at its Plant No. 2 site in Huntington Beach, where much of the county's treated wastewater is discharged into the Pacific Ocean through a 10-foot-diameter outfall pipeline that extends five miles out to sea. The district also will be rehabilitating its "short" outfall pipeline (a one-mile-long standby pipeline that carries treated wastewater out to sea when the primary pipeline is not in service), and one of OCSD's surge towers, which help control pressure surges in the wastewater system.

The Final Effluent Sampler Building at Plant No. 2 houses the equipment that the district's water-treatment specialists use to collect samples of the final effluent before the outfall is released into the ocean. While OCSD has performed various modifications and rehabilitations to the building and its equipment during the last 20 years, the useful life of the building and its equipment has come to an end. Therefore, OCSD has begun the process of removing the current building and its outdated equipment, constructing a new building, and installing a new effluent sampler pumping system and sampling ports. OCSD also will restore the surrounding landscape and improve the site's drainage.

The Atkins team will provide detailed inspection and comprehensive rehabilitation planning services for the short outfall pipeline and Surge Tower No. 1. Atkins also will assess, specify, and participate in installation of the new sampling equipment for the new Final Effluent Sampler Building. Additionally, Atkins will inspect and develop rehabilitation plans for more than 14,000 feet of underground utility tunnels that serve OCSD's facilities.

Information provided by Atkins

Atkins will provide detailed inspection and comprehensive rehabilitation planning services for one of the Orange County Sanitation District's surge towers, which help control pressure surges in the wastewater system.

Submit news and photos of planned, ongoing, or recently completed projects to Bob Drake at In March, "Project Notes" will highlight use of geosynthetics and GIS; in April, mining/energy and geotechnology are the focus.

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