MICROPILE FOUNDATIONS FOR RECONSTRUCTION OF HISTORIC LA LOMA BRIDGE IN PASADENA, CALIFORNIA-Paper

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The La Loma Bridge, a 1914 Neoclassical bridge over the Arroyo Seco in Pasadena, was listed on the National Register of Historic Places in 2004. Concrete deterioration and seismic vulnerability prompted a reconstruction designed to preserve its historic appearance: a new bridge structure would be built within the existing arches and spandrel columns, which would remain as the visible façade.<br /><br />Limited access in the canyon, nearby trails and vegetation, and the need to minimize disturbance to the historic structure made micropiles a suitable foundation solution. Forty micropiles were installed to support the new pier footings. Each was designed for 270 kips in compression and 45 kips in tension, using a reinforcing bar, steel casing through existing footings where needed, and a 24-foot bond length in bedrock. The site’s bedrock comprised quartz diorite on one side of the Eagle Rock Fault and sandstone conglomerate on the other.<br /><br />A compact drill rig and down-the-hole hammer were used to install the piles in the confined work area. Four preconstruction verification piles and eight production piles were tested in tension to 540 kips—twice the design compression load. All tests met the project’s movement, load-displacement, and creep acceptance criteria.<br /><br />Completed in October 2015, the micropile work demonstrated that foundations could be installed beside the existing bridge columns with minimal disruption, enabling construction of the new structure while retaining the original bridge’s historic character.

Keywords

La Loma Bridge

Pasadena

historic bridge reconstruction

National Register of Historic Places

micropiles

seismic vulnerability

Neoclassical bridge

bedrock foundation

load testing

historic preservation