Design, Installation and Performance of Earth Retention System to Limit Ground Movements Around Sensitive Structures in Washington, DC-Technical Paper Upload

Technical Paper Upload

Pdf Summary

The Scottish Rites Apartments project in Washington, DC required a 40-foot-deep excavation beside the historic House of the Temple, a 19th-century Carriage House, and a four-story brick townhouse. The site’s challenging geology included loose fill and alluvial soils over dense Potomac Formation deposits containing abrasive gravel, cobbles, and boulders. Groundwater and leaks from existing sewers added construction challenges.<br /><br />The temporary earth retention system used driven steel soldier beams, timber lagging, and tiebacks. To limit movement and protect nearby structures, the design incorporated movement-based analysis and three tieback levels near the most sensitive buildings. Soldier beams were installed with a variable-moment vibratory hammer, while vibration and building movement were continuously monitored. Tiebacks and permanent foundation micropiles were drilled using rotary methods and down-the-hole hammers to penetrate the dense, obstructed soils. Load testing confirmed strong anchor and micropile bond capacity.<br /><br />Performance was successful: soldier beam lateral movement was generally no more than 0.5 inches, and most beams settled less than 0.25 inches. The House of the Temple and townhouse experienced no settlement or tilt; the Carriage House settled no more than 1/32 inch. No new cracks or visible structural damage occurred, despite occasional brief vibration readings above project thresholds.<br /><br />The case history demonstrates that movement-sensitive excavation in dense, boulder-laden urban soils can be completed safely through careful design, vibration-conscious equipment, close monitoring, and construction practices that minimize ground loss. Micropiles were also installed successfully as permanent foundation elements.

Keywords

Scottish Rites Apartments

Washington DC excavation

earth retention system

soldier beams

timber lagging

tiebacks

micropiles

vibration monitoring

historic structures protection

Potomac Formation soils