Bridging the Gap at Armistead Point Golf Community

  For a true test of segmental retaining wall strength, few projects are more demanding than land bridges. At Armistead Point, engineers designed a land bridge that is 240 feet (73 meters) long and 15 feet (4.6 meters) wide, and provides a 250 psf (1,220 kg/m2) traffic live load at its crest. A load transfer platform and a retaining wall system were chosen for the wall.

The Armistead Point Golf Community is an exclusive, gated golf course community in historic Williamsburg, Virginia. The owner sought to develop the site, located along the James River, while maintaining the historic charm of Williamsburg. The property was divided by a large creek and underlain by a deep peat deposit. Excavating the peat was deemed too costly. In order to adjoin the divided properties and access the property along the James River, a steel bridge was originally proposed to cross the creek. There were two problems with this proposed solution: The first was a steel shortage that resulted in higher than anticipated steel costs and a longer than anticipated delivery time. Secondly, a steel bridge would not have offered an aesthetic appearance complementing the historic charm of Williamsburg.

The best solution presented to the owner was an option to build a land bridge constructed with back-to-back segmental retaining wall (SRW) systems. This option provided a solution that was cost-effective, was structurally sound and met the aesthetic needs of the owner. In order to provide foundation support for the land bridge and retaining walls, a load-transfer platform was incorporated into the project. The load-transfer platform consisted of auger-cast piles driven through the deep peat deposit and a platform consisting of geosynthetic-reinforced gravel to bridge the piles. The twin walls, each measuring 240 feet (73 meters) long and 15 feet (4.6 meters) high accommodated a storm water drain pipe running perpendicular to the wall at its base along with a 250-psf (1,220 kg/m2) traffic live load at its crest. The total area of the project is 18,000 square feet (1,672 m2) of wall.

The land bridge solution using SRW units, combined with the load-transfer platform offered a 50-percent cost savings as compared to the proposed steel bridge. The blended, earth tone colors and unique, rustic appearance led to other applications on the project such as pillars and the entrance sign on the property. The SRW products also provided proven structural performance while capturing the historic and natural beauty of Williamsburg. CMD

   

Engineer
Engineering Consulting Services, LTD, Richmond, VA

Foundation Design Engineer
The Collin Group, Bethesda, MD

Wall Contractor
Force Construction, Millersville, MD

Wall Installer
Easton Block Retaining Walls, Skippack, PA

SRW Producer
Allied Concrete Products, Richmond, VA

 

 

 

 

 

 

 

 

 

 

 

Marginal Soils

As with any structure, SRWs must be supported by foundation materials with sufficient capacity against the loads of the structure and that are adequate enough to avoid excessive settlement beneath the SRW. Unsuitable foundation conditions at the planned base elevation of the wall should be addressed like on other structures by the geotechnical engineer of the project that may include one or a combination of the following techniques:

  • Excavate and replace unsuitable soils with adequate oversizing of the excavation.
  • Locate base of SRW at competent soil.
  • Expand the aggregate leveling pad width and thickness.
  • Reinforce a thickened aggregate leveling pad with geogrid.
  • Preload the area prior to wall construction.
  • Preload wall prior to paving or building construction above wall.
  • Employ soil improvement techniques: vibrocompaction, stone columns, dynamic compaction, etc.

All areas below a SRW system that have bearing capacity or settlement issues should be addressed. In the case of reinforced SRWs, the reinforced soil zone may be adding as much new load to the foundation as the SRW units do at the face of the wall. So foundation materials below the reinforced soil zone may need to be improved as well as the area directly below the SRW unit wall face.