Railway Wall Construction

THE CHALLENGE

When the Aquila Dock coal handling facility needed to expand its rail lines, construction plans required an additional 15 to 20 feet (4.5 to 6 meters) of level land. The challenge? The site of the proposed line was located on a steep grade between an existing covered railway bridge and a live Norfolk Southern railway.

The location left Aquila Dock with very few options for creating a level space for the new line, as room for excavation and reinforcing any sort of wall was extremely limited. The project required a 21-foot-high (6.4-meter-high), but the tight footprint wouldn’t allow equipment for piling, and the undercutting necessary for a grid-reinforced wall would require shutting down the rail line.

Aquila Dock officials decided that a Redi-Rock gravity wall would be the best choice for the project. The setback of the wall allowed the design to be built as a gravity structure to fit the site’s tight footprint and kept other rail lines in service during the project.

THE SOLUTION

Aquila Dock worked with Brad Turman, P.E. on the preliminary design of the wall. The design criteria included the construction of a 4,500 square foot (418 square meter) Redi-Rock gravity retaining wall at the bottom of the slope and backfilled to create an additional 15 to 20 feet (4.5 to 6 meters) of level ground at the top of the wall. The wall would support an additional track approximately 16 feet (4.8 meters) back from the wall face. Train traffic on this section would be slow, about two to five miles per hour (3.2 to 5 kilometers per hour).

Redi-Rock’s massive, precast concrete retaining wall blocks weigh over one ton each to achieve tall gravity walls without the use of geogrid and the extensive excavation that goes with it. Turnman recommended a Redi-Rock design solution that met the height, geometry, and load conditions required by this site. The design included a reinforced concrete leveling pad with a concrete shear key at the toe to help resist sliding forces. The toe of the wall started 18 feet (5.5 meters) below an overhang for the adjacent covered rail bridge. To achieve the necessary height, the wall design included 60in (1520mm) bottom blocks, followed by 60in (1520mm) middle blocks, then 9in (230mm) setback blocks, and finished with 28in (710mm) middle and top blocks. The wall was completely backfilled with imported ¾ inch (19 millimeter) limestone on a 1:1 influence beginning at the leveling pad and extending the full wall height.

Redi-Rock 9in setback blocks allowed the increase of the design batter to approximately 26.6 degrees for the gravity structure ensuring that the wall cleared the canopy at the top. The 9in setback block enabled the project to meet safety factors with respect to overturning and provided the geometry needed for the predetermined project footprint.

THE INSTALLATION

Foster Supply began construction of the Redi-Rock wall with the assistance of subcontractors J.R. Contractors in 2008. Redi-Rock installs like giant Legos-each block interlocking with the one above through a system of knobs and grooves. The blocks were installed using a single piece of heavy machinery and a small crew. With limited access to the site, the crew had very little space to stage equipment or store material. Because construction had to take place while the adjacent railway was live, material had to be stored remotely and transported onsite piecemeal.

THE OUTCOME

The finished wall measured approximately 4,500 square foot (418 square meter) with the tallest section standing 21 feet (6.4 meters) tall and stretching approximately 260 feet (50 meters) long. The completed wall incorporated both Redi-Rock Cobblestone and Limestone textures.

PROJECT DETAILS

Project: Railway Expansion #117 Customer: Aquila Dock Installers: Foster Supply, Inc. and J.R. Contractors Location: Kenova, West Virginia