Marine Foundation Retrofit for the Richmond-San Rafael Bridge-PDF

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The Richmond–San Rafael Bridge seismic upgrade included extensive retrofits to its submerged foundations and replacement of the West Trestle. The marine work comprised 476 tension and compression micropiles installed through existing pier foundations, large CISS and CIDH shear piles connected through precast concrete pile-cap extensions, and 132 new 66-inch CIDH piles for the replacement viaduct. Work was generally performed underwater and often in restricted-headroom conditions.<br /><br />Subsurface conditions varied considerably. The bay mud was very soft, bedrock depth ranged from 15 to 200 feet below the mudline, and bedrock included fractured chert, shale, and greywacke. These conditions complicated drilling and pile installation, particularly where dense sands masked the point at which steel shells reached bedrock.<br /><br />Micropiles were cored through the existing bell piers using rigid templates to maintain alignment around existing piles. Only eight of the 476 planned micropiles could not be installed because of obstructions. Testing identified higher-than-expected deflections in some piles; adding central reinforcing bars and revising the analyses helped address the issue.<br /><br />Shear-pile construction involved setting barge-delivered precast pile caps, installing support piles, and lowering large steel shells through pile-cap sleeves. CIDH rock sockets were drilled under slurry support and filled with tremie concrete. One unstable socket was successfully remediated by backfilling, redrilling, and using fiber-reinforced concrete. Sonic testing found only minor anomalies.<br /><br />For the new viaduct, 66-inch steel shells were installed from barges or a temporary trestle, with rock sockets drilled and reinforced. In some locations, dense overlying sands made it difficult to identify bedrock and caused shell tips to deform; smaller sockets or drilling through the tips resolved these cases. The paper describes the specialized design details, marine equipment, and construction adaptations that enabled the foundation retrofit to be completed.

Keywords

Richmond-San Rafael Bridge

seismic upgrade

submerged foundations

micropiles

CIDH piles

CISS shear piles

marine construction

bedrock drilling

pile-cap extensions

foundation retrofit