SANDAG requests modifications to Del Mar bluff project

Three modifications to the railroad bluffs stabilization project underway in Del Mar will be considered at the California Coastal Commission’s virtual meeting July 10.

The San Diego Association of Governments has asked the commission for approval to increase the height of a retaining wall by three feet at the bottom of the bluff near 12th Street, install four additional soldier piles on the upper bluff near 12th Street, and repair erosion on the upper bluff near Seventh Street.

Work began in mid-May and is expected to continue through the summer on the fourth phase of bluff stabilization projects in Del Mar, where coastal erosion is a constant threat to the cliff-top tracks. The route is a vital link in the 351-mile-long Los Angeles-San Diego-San Luis Obispo rail corridor, which carries nearly $1 billion in freight and millions of passengers every year.

Coastal Commission staffers have reviewed the proposed modifications and recommend approval, according to their report.

The wooden retaining wall at the base of the bluffs is being reinforced with new galvanized steel H-beams and new timber lagging between the beams, under a design approved previously. The new beams will be set in a concrete foundation 15 feet deep, and with the requested amendment the new wall will be nine feet tall, the staff report states.

The purpose of the 360-foot-long wall is to prevent waves from undermining the bluffs, which would lead to landslides on the upper slope.

The upper slope has an unstable gap of about 20 feet between soldier piles installed in 2008 and a concrete buttress built in 1998. Soldier piles are made by placing steel H-beams in holes of various depths and filling the holes with concrete to reinforce the slope.

An earlier plan called for 13 soldier piles, which the modification would increase to 17, to shore up the gap and strengthen the deteriorating concrete buttress. The piles are about 11 feet west of the centerline of the track.

Storm runoff during the winter of 2019 eroded several areas along the bluff, some of which were repaired immediately. The additional areas to be repaired are two 20-foot-wide sections below the track near Seventh Street. They will be trimmed, cleaned and filled with decomposed granite, reinforced with fabric.

Long-term plans call for the tracks to eventually be re-routed through inland tunnels around the 1.6 miles of Del Mar bluff. However, that solution will cost more than $3 billion and is decades away.

-- Phil Diehl is a reporter for The San Diego Union-Tribune