The Elephant Trunk, Highway 1: Stabilization of a Steep Coastline using permanent DYWIDAG Strand Anchors

Near the northern border of San Luis Obispo County in southern California, Highway 1 is located in the immediate vicinity of a rocky bluff. Through an area known as the Elephant Trunk along this route, the Pacific coast is characterized by unstable geology. Major landslides and settlements occurred time and again in this area, which is why repair work was required on a regular basis.

In order to permanently stabilize this area, a soldier pile wall was constructed in this section below the route, and Highway 1 was straightened. The lanes are being widened from 3.35m to 3.65m (11 to 12ft), and an additional 1.2m (4ft) wide hard shoulder is being built.

To prevent possible rock falls from the steep coast above the road, a 0.60 to 1.2m (2-4ft) wide catchment area was built for falling debris, and the existing drainage system was optimized and repaired.

The new soldier pile wall has a total length of approximately 305m (1,000ft). On the surface, only a part of the maximum 15m (50ft) high retaining wall is visible.

The steel girders of the soldier pile wall were tied back to the stable slope strata using permanent DYWIDAG Strand Anchors. To tie back the retaining wall, DSI Construction USA supplied 259 Type 5-0.6" and 6-0.6" DYWIDAG Strand Anchors.

The DYWIDAG Strand Anchor System was especially suitable for use due to its high degree of flexibility with regards to the required anchor lengths. As construction and storage space was limited, the anchors were supplied to the jobsite on coils, thus minimizing space requirements.


Caltrans (California Department of Transportation), USA

General Contractor

John Madonna Construction Co., Inc., USA


Drill Tech Drilling & Shoring Inc., USA


Caltrans (California Department of Transportation), USA

DSI Unit

DYWIDAG-Systems International USA Inc., BU Geotechnics, USA

DSI Scope

Production, supply

DYWIDAG Products

259 Type 5-0.6" and 6-0.6" permanent DYWIDAG Strand Anchors

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