The city of Newport, RI, had an existing section of retaining wall along the famed Ocean Avenue that needed to be replaced to ensure continued safe operation of the roadway. The failing 300-foot-long wall was built during the 1930s as part of the Works Progress Administration program. It was a typical robust cast-in-place design, which was standard practice for sea walls at that time. Chemical breakdown of the concrete and reinforcing steel, as well as of the steel scupper pipes within the wall, and severe erosion behind the wall near its midpoint led to the need for replacement or rehabilitation.
The critical section of the wall, which drove the redesign of the entire wall, was at the closest point to Ocean Avenue. This was also, incidentally, the highest section of wall. Small volumes of seawater were being retained for a period of time behind the concrete in this location during storm events, and this had contributed to the structural failure of the wall throughout this area. Severe erosion had also taken place during wave overtopping, which needed to be accounted for in any new design. Because of time constraints as well as uncertainty as to the best design for the new wall, the city decided to solicit design/build proposals for the replacement of this important structure. Funding for the project came from the Federal Highway Administration, with the Rhode Island Department of Transportation acting as the liaison. Therefore, any materials used for a rehabilitation or replacement had to be approved at the state and federal levels.
A team consisting of Mello Construction Co. Inc.; William Young, P.E., of Contech Engineered Solutions; Gary Munkelt, P.E., of Gary K. Munkelt & Associates; and Greg Stratis of Shea Concrete Products came together to present a complete replacement proposal to the city of Newport. John Mello of Mello Construction Co. attended a presentation on innovative infrastructure solutions featuring retaining walls and erosion control solutions presented by William Young of Contech and Arthur Erhardt of GridTech Inc., and he immediately approached them and said, “Let’s go win a sea wall project together.” Of the several teams who submitted proposals, they were the only team that offered a complete replacement of the existing wall. The team, led by William Young, agreed that a hybrid ReCon gravity/positively connected MSE retaining wall system using high-strength Tensar geogrids and Armorflex erosion control materials would ultimately be the most sustainable, most cost-effective, and least disruptive method of replacing this sea wall. The goal of the team was to design a wall that could be built by an excavation contractor working around low tides, preferably with zero cast-in-place concrete. The benefits would be realized in greatly reduced labor costs, scheduling flexibility, and a highly sustainable design featuring no steel, and, ultimately, no long-term corrosion.
The design presented, and ultimately selected, used the latest technology in the following areas:
- Wet-cast, precast, saltwater concrete mix cast in a fully controlled environment
- High-strength and highly sustainable polypropylene geogrid and innovative MSE/GRS design techniques
- Innovative erosion control via vegetated green hard-armor design and materials
The retaining wall blocks chosen were the ReCon wet-cast modular retaining wall blocks manufactured by Shea Concrete Products. These blocks measure 48 inches long by 16 inches high and run up to 60 inches in depth. These wet-cast blocks use a special mix design supplied by Shea Concrete that was created to withstand the adverse effects of saltwater with a service life in excess of 75 years. Gary Munkelt envisioned a wall that would allow for the immediate dissipation of hydrostatic surcharge in back of the wall created by a wave crashing over the top. It was imperative that the stone behind the wall be able to completely drain before the next ocean swell crashed over the top. Most retaining wall systems consist of weep holes spaced equidistantly along the bottom the wall, but in this situation, a far quicker draining solution had to be implemented. Greg Stratis of Shea Concrete pointed out that the ReCon block was designed with a taper at the front face of the block and a natural rounded texture in each of the four corners of the block, which would allow for just such drainage.
The top block implemented in the design weighed approximately 5,800 pounds and was originally developed by Shea Concrete as a moment slab style block to resist overturning with a vehicular guardrail attached to it. The purpose of this enormous block on top of the sea wall was threefold. The first was to stabilize the top of the wall against the uplift forces of a wave crashing into the wall. The second was to provide a receiving channel for the ArmorLoc hard-armor erosion protection mat, and the third was to increase the dead load on the bottom of the wall, resulting in increased frictional resistance against sliding.
The reinforcing grids used were Tensar biaxial and uniaxial high-strength geogrids. These grids are made of extruded polypropylene resin. The uniaxial grid was used to create a massive contiguous wall section positively attached to the crushed stone in back of the wall. A special 18-inch-long “tab” section of the grid was cast into the back of the lower blocks and then again into the back of the top blocks of the wall, creating a 100% positive connection between the face of the wall and the stone mass behind. The tab on the lower block was then connected to a longer section of grid during the wall construction process. Crushed stone was placed behind the ReCon blocks to the back of the excavation zone, and the grids were then pulled up and over the top of the filled crushed stone area and connected to the tab in the top block. The biaxial grid was used as a gabion-like cage beneath and behind the wall to contain the crushed stone from the constant pulling forces created by the water entering and exiting the wall during wave impact.
The top of the wall was protected in critical areas using ArmorFlex articulating concrete blocks. These blocks will protect the finished top of the wall back to Ocean Avenue from surface erosion in the event of wave overtopping. Best of all, this hard armor can be completely vegetated to bring back the soft look that existed before the severe erosion took place.
Work on the project began in the summer of 2011. Removal of the existing wall was followed by the excavation of a keyway trench into the underlying bedrock. Ultimately, a cast-in-place leveling pad or mud slab was built along the center portion of the wall, upon which the ReCon blocks were set. Ocean Avenue remained open during the construction of the new wall.
The wall was completed in mid-August, just before Hurricane Irene visited the Rhode Island coast. The wall had a second and much more intense test with the arrival of Hurricane Sandy in October 2012, during which the wall was completely overtopped during the storm surges.
The use of the large wet-cast ReCon block in combination with Tensar grids and ArmorFlex hard armor, all of which were distributed by Contech Engineered Solutions, resulted in a unique, cost-effective, and highly efficient design that is now standing up to the pounding that the open Atlantic Ocean constantly delivers.
