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

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The 34-story Landmark Apartment tower in West Los Angeles was built within the footprint of an existing parking structure with four basement levels. Because the new tower’s heavier column loads could cause settlement that might affect the existing spread-footing foundations, it was supported on cast-in-drilled-hole (CIDH) piles instead. The 4-foot-diameter shafts extended 65–90 feet below the pile caps and were installed using drilling mud through saturated alluvial soils.<br /><br />Construction required cutting a large opening, or “glory-hole,” through the existing basement floors. Since those floors had provided lateral support to a nearby basement wall, temporary bracing was needed before demolition. Property and right-of-way constraints limited the use of tie-back anchors alone, so the wall was supported by rakers founded on micropiles and supplemented by tie-back anchors. This temporary foundation system occupied space within the new tower footprint, requiring the permanent pile cap to be divided into two sections, with temporary anchors routed between the permanent drilled shafts.<br /><br />Groundwater was already managed by the parking structure’s permanent drainage system, but deeper excavations for new foundations required additional temporary dewatering. Existing footings near the new pile caps were underpinned as needed, and the structure was monitored during demolition and construction. The temporary anchors and rakers were preloaded to transfer wall loads away from the existing floor slabs before those slabs were removed.<br /><br />Once the new piles, pile caps, and floor diaphragms were completed, the temporary shoring was unloaded and dismantled. The project demonstrates how coordinated foundation design, shoring, dewatering, monitoring, and construction sequencing enabled a high-rise to be built within an occupied building’s existing footprint while meeting foundation and seismic performance requirements.

Keywords

Landmark Apartment tower

West Los Angeles

CIDH piles

cast-in-drilled-hole piles

deep foundations

temporary shoring

micropiles

dewatering

glory-hole excavation

pile caps