2100 L Street Underpinning & Support of Excavation-PPT Presentation

PPT Presentation

Pdf Summary

The 2100 L Street project involved underpinning neighboring buildings and supporting deep excavations in three areas: the Gelman Building, the L and 21st Street frontages, and Stevens School.<br /><br />The eight-story Gelman Building has three basement levels and foundations bearing on rock. Underpinning requirements were negotiated with the property owners, who permitted brackets beneath the existing wall footing and rock bolts or tiebacks beneath the building. Bracket piles—drilled and socketed into rock, then dry-packed to the footing—provided an economical support method. The presentation also reported lateral and vertical movement monitoring.<br /><br />Along L and 21st Streets, excavation support had to accommodate numerous utilities extending to about 22 feet below grade and challenging site conditions. The system used round HSS rakers and cross-lot bracing against wales for upper-level support, with tiebacks anchored into rock at lower levels. The dense bracing and steep grade changes complicated excavation and construction.<br /><br />Stevens School, a late-19th-century brick building, had heavy exterior wall loads carried by corbelled brick footings on rubble concrete. Because the new building required support directly along the wall line, the team developed a soil-cement underpinning beam to reduce the hazard of working beneath potentially weak existing foundations. The beam was installed beneath the footing and subsequently supported by hand-dug concrete piers extending to rock. Other methods used on the project included micropiles, rock bolting, and shotcrete.<br /><br />Overall, the work required tailored solutions to protect adjacent structures while accommodating limited space, heavy loads, utilities, and varying ground and foundation conditions.

Keywords

underpinning

deep excavation

Gelman Building

tiebacks

rock bolts

cross-lot bracing

HSS rakers

micropiles

soil-cement beam

adjacent structures