Underpinning of Historic Structures-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes underpinning and foundation work for two historic-building projects in Washington, DC: the City Ridge development and renovation of the Milken Center.<br /><br />At City Ridge, eight new buildings, residential and hotel space, retail and offices, and a large underground parking structure were planned around an existing building. Construction required lowering the ground floor, excavating for parking, and supporting the historic structure. Because of high loads, strict settlement limits, difficult access, and low headroom, engineers installed 385 steel-cased micropiles: 7-inch piles beneath gravity-load columns and 9⅝-inch piles at braced-frame locations. Each had a 100-ton allowable compression capacity and was tested to a maximum of 250 tons. Loads were transferred from existing columns to the micropiles using welded brackets, transfer beams, and hydraulic jacks; BIM coordination supported integration with excavation and new construction.<br /><br />The site’s deep foundations relied mainly on weathered and less-weathered rock. Excavation support included a temporary soil-nail wall and a perimeter soldier-pile-and-lagging wall, supported by tiebacks where possible and internal bracing where tiebacks could not be used.<br /><br />At the Milken Center, renovation included replacing an upper level with two new levels and lowering the basement by up to 4.5 feet. More than 300 large-diameter micropiles were installed under low-headroom conditions to temporarily support an interior bearing wall. Needle beams, transfer beams, and 16 shoring towers carried the wall loads. Towers were preloaded sequentially with hydraulic jacks to avoid concentrating loads on the existing wall. The micropiles were then connected to new pile caps using headed shear studs.<br /><br />Together, the projects demonstrate how carefully staged load transfer, micropiles, excavation support, and close coordination can enable major construction and renovation beside or within historic structures.

Keywords

micropiles

historic building renovation

underpinning

foundation work

Washington DC

excavation support

load transfer

shoring towers

soil-nail wall

soldier-pile wall