The Mayor and the Geotechnical Engineer – Challenges Obtaining Approval For Use of Alternative Fill Materials to Accommodate Sea Level Rise in the City of San Francisco-Paper

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Mission Rock is a new waterfront neighborhood in San Francisco, built on reclaimed land over thick, compressible Bay Mud. The project’s public streets and infrastructure needed to be raised about 66 inches to accommodate projected sea-level rise by 2100. Conventional soil fill would have added enough weight to trigger up to 24 inches of consolidation settlement, conflicting with the developers’ goal of a resilient, low-settlement site.<br /><br />The design team selected lightweight cellular concrete (LCC), using excavation of existing fill to offset new loads. However, LCC was not an approved fill material for San Francisco’s public right-of-way, and agencies raised concerns about its strength under traffic, ease of excavation for utility work, resistance to hydrostatic uplift, earthquake performance, increased weight when saturated, and future availability and competition among suppliers.<br /><br />Approval required coordinated technical and political effort. The team conducted peer reviews, convened a technical advisory panel, developed specifications, and addressed agency comments through frequent meetings. A full-scale roadway mock-up was built and tested: it was flooded to assess uplift resistance, driven over by a hook-and-ladder fire truck, and then excavated. The tests were successful. The team also selected non-permeable LCC to address concerns about patents and limited suppliers.<br /><br />After the Mayor helped secure agreement among senior decision-makers, further requirements remained, including final calculations and specifications, quality-control procedures, a 10-year monitoring plan, performance guarantees, and a Port Director’s Order authorizing the material as a deviation from standard requirements. The permit was issued 22 months after the initial request.<br /><br />The authors conclude that adopting new materials requires substantial engineering, testing, review, and long-term monitoring, with associated time and cost. Public benefits and committed project sponsors are important, while political leadership can help bring agencies together. The Mission Rock evaluation has since helped streamline LCC approvals for other Bay Area projects.

Keywords

Mission Rock

San Francisco

waterfront neighborhood

reclaimed land

Bay Mud

sea-level rise

lightweight cellular concrete

consolidation settlement

roadway mock-up

public right-of-way