Deep Foundations for High-Rise Building Within Footprint of Existing Parking Structure

The Landmark Apartment building is a 34-story high-rise constructed in West Los Angeles. The high-rise was constructed within a portion of the footprint of an existing parking structure with four subterranean levels. The foundations of the new high-rise were cast-in-place drilled hole (CIDH) piles in order to limit settlement of the new construction relative to the existing parking structure spread footing foundations. In order to construct within the parking structure, a gloryhole had to be cut in the parking structure at the location of the new high-rise footprint, necessitating temporary bracing of the parking structure basement walls. The temporary bracing had to be accomplished using both tie-back anchors and internal bracing (rakers) in order to provide lateral restraint for the basement wall. The internal bracing required its own set of foundations, including micropiles and tie-back anchors to laterally restrain the micropile caps. The foundation system for the new high-rise had to be split into two major pile caps on either side of the temporary micropile cap foundation for the bracing system, with the temporary micropile cap tie-back anchors threading between the permanent structure drilled shafts. In addition, groundwater was located just beneath the bottom-most slab of the parking structure, requiring dewatering of pile cap excavations. With high groundwater conditions, drilling mud was required to install the CIDH piles. These design challenges were accomplished successfully and meeting the requirements for foundation performance and seismic performance of the structure. The multiple challenges of temporary works also required careful coordination of dewatering, shoring installation, and foundation installation among the various disciplines.