Saving the Old While Building the New: A Geotechnical Approach to Historic Structure Preservation

by Jody Wall, P.E., Carolina Stalite Company

Many of us around the country have visited Savannah, Charleston and other old southern cities. They are true gems, full of old and very beautiful historic buildings. The downtown areas have buildings from a bygone era that would be hard to duplicate today and strolling through them is like takingNew Roadway Construction: Protection of Storm Water Outfalls (Washington, DC) a walk through time. But like so many places, not all the historic structures are above ground. Some of the structures are never really seen but play a crucial role in how the cities operate.

New construction in such grand old cities comes with difficulties for designers and engineers. The protection of historic structures both above and below ground is a part of most design analyses. So what do engineers do when the demands for today create excess loads on historic structures? It is not an uncommon occurrence; we have been involved in a multitude of projects where the loads on historic structures both above and below ground need to be reduced. In one project, there was 20 feet of new fill going over storm water drainage outfall structures that were constructed in the 1850’s. In another case, there was an elevation change of 5 feet in an intersection/road extension with concrete storm sewer structures running below them. In a third case, there was a grade change of 4 feet for new road construction with an underlying storm sewer system.

The solution to these projects and many more was to use lightweight aggregate fill to reduce the design load on the structures to increase the factor of safety and minimize the threat to the historic structures. In each of the cases shown above, the choice between replacing or reinforcing the structures compared to the use of lightweight aggregate to minimize the loads made the choice obvious. The loads were reduced by half or more in each application and the net result was a load condition that was acceptable without modification to the structures. The ease, speed and cost effectiveness of lightweight aggregate fill allows engineers to meet both their design intent for the new construction and project budget constraints, while not jeopardizing the historic underground structures.

The key design features of ESCS Lightweight aggregate fill which make it the choice of so many in these applications include:

  • Lower Density – less than half of most fill materials
  • High internal angle of friction
  • Resistivity, pH, Sulfates and Chlorides that meet FHWA MSE Wall requirements
  • Acid and chemical insolubility
  • Resistance to freeze thaw damage

Photo Gallery

  • New Roadway Construction: Protection of Underground Water Structures (Miami, FL)
  • Existing Roadway Modifications: Grade Change Over Storm Water Structure (Savannah, GA)