Restoring Coast Boulevard Above La Jolla’s Failing Sea Cave

In August 2019, the City of San Diego confronted an unusual infrastructure emergency beneath one of La Jolla’s most recognizable coastal streets. A sea cave extending below Coast Boulevard had deteriorated to the point that engineers feared its roof could collapse without warning, potentially creating a sinkhole beneath the roadway.

The cave—identified in different records as Cook’s Crack, Koch’s Cave, and the Coast Boulevard sea cave—was located near 1210 Coast Boulevard, only a short distance from La Jolla Cove. Continued wave action, groundwater, erosion, and falling material had weakened the cave’s interior and the ground supporting the street above it.

On August 8, 2019, the City closed the affected section of Coast Boulevard. Emergency construction began the following day.

Stabilizing the Ground from Below

The Coast Boulevard Sea Cave Emergency Stabilization Project required crews to work in an exceptionally constrained environment. The site was surrounded by steep bluffs and sensitive marine habitat, while tides and surf repeatedly changed conditions at the cave entrance. Contractors also had to limit disruptions to nearby residents, businesses, and the many visitors drawn to the La Jolla coastline.

Initial work included injecting polymer-based grout beneath the road to strengthen the soil above the cave. Crews installed a temporary breakwater at the cave entrance to reduce wave energy and provide safer working conditions. Access and ventilation openings were drilled through the roadway, while marine personnel removed sand and debris from inside the cave.

The underground void was then filled with a controlled low-strength sand-and-cement slurry. The material was formulated to stabilize the roadway while remaining compatible with the surrounding coastal formation. The project also included drainage and water-quality improvements, including a biofiltration system for treating runoff before discharge.

Once the underground emergency work had secured the roadway, attention turned to reconstructing the heavily impacted surface of Coast Boulevard.

Alvarez and Shaw’s Role: Rebuilding the Roadway

Flatiron West, Inc., the project’s emergency design-build contractor, selected Alvarez and Shaw, Inc. to perform paving services for the Cook’s Cave Emergency Project. The subcontract became effective on September 18, 2019.

Alvarez and Shaw’s work centered on restoring the concrete street above and around the stabilized cave. Company field records document crews setting pavement forms, coordinating concrete pumping, placing and finishing the roadway concrete, creating the required stamped surface, saw-cutting joints, and completing final cleanup.

The paving operation required much more than placing a single concrete slab. Coast Boulevard follows a sweeping horizontal curve while its surface elevations change along the bluff. The reconstructed pavement had to connect precisely with the existing roadway, sidewalks, drainage structures, utility frames, and adjacent improvements.

The project’s paving plan divided the restoration into four principal pours totaling approximately 408 cubic yards. It also called for about 7,665 square feet of stamped concrete patterned to match the street’s existing 12-by-6-inch brick appearance. Maintaining that historic-looking finish across curved pavement panels required careful layout and sequencing.

Concrete placement and stamping then proceeded through a succession of carefully managed pours, with crews, pumps, finishers, suppliers, and specialty saw-cutting services coordinated around a compressed emergency schedule.

This surface restoration was a critical final stage of the larger stabilization effort. Although the most dramatic work occurred beneath the road and inside the cave, Coast Boulevard could not reopen until the street was reconstructed to provide a safe, durable, and visually compatible public surface.

Completing an Emergency Project Ahead of Schedule

Coast Boulevard reopened on October 15, 2019, after a 68-day closure and ahead of the City’s original November completion estimate. Vehicular and pedestrian access was restored, and the finished pavement preserved the distinctive character of the coastal roadway.

The project later received major industry recognition. Engineering News-Record named it a 2020 California Best Project in the Small Project category and subsequently selected it as the national Best of the Best winner for Small Projects. ENR’s project-team listing identifies Alvarez and Shaw among the subcontractors that contributed to the award-winning result.

For Alvarez and Shaw, the project demonstrated the company’s ability to mobilize quickly, coordinate multiple concrete operations, and deliver specialized paving under emergency conditions. Its crews helped transform a disrupted construction zone back into a safe, finished public roadway—one whose patterned concrete surface conceals the extraordinary stabilization work beneath it.

Today, thousands of people travel along Coast Boulevard without seeing the repaired cave below. What they do see is the completed roadway: formed, poured, finished, and stamped as part of Alvarez and Shaw’s contribution to preserving one of San Diego’s most valued coastal routes.

City of San Diego project page, California Coastal Commission report, and Engineering News-Record’s project profile.