A block-glide debris-fall landslide occurred on February 22,1993, within a 30.5-m (lOO-ft)-high bluff in the Capistrano Beach area in the cities of Dana Point and San Clemente, Orange County, California. Five homes were destroyed, and several others remained in jeopardy subsequent to this catastrophic ground failure. The landslide caused the bluff top to retreat a maximum of 24.4 m (80 ft) and deposited 20,000 m3 (27,000 cy3) of landslide debris up to 10.5 m (35 ft) deep on Pacific Coast Highway (PCH), a designated emergency evacuation route for the San Onofre nuclear-powered electricity generating station. The landslide debris also covered a 76.2-m (250-ft) sec-tion of the only rail line linking the Los Angeles/Orange County area with San Diego.

The winter storms preceding this landslide brought 53.3 cm (21 in) of rain to the Capistrano Beach area. The single-month peak of 29 cm (11.44 in) occurred in January and was the highest in 30 yr. This excessive rainfall infiltrated the subsurface, trig-gering the landslide, which failed on an adverse-dipping clay bed at approximately midslope of the 30.5-m (lOO-ft)-high bluffs. The landslide scarp was controlled by high-angle bedrock jointing.

Mitigation alternatives were restrictive because of the many public/private landowners involved and the fact that the city boundary between Dana Point and San Clemente is located in the upper part of the bluff. Initially, the various stabilization options considered to reopen PCH were restricted within the jurisdiction of Dana Point. Eventually, the failed portion of the bluff was restored by a system of rock-bolt tiebacks combined with a hardface wall and buttressed slope. Subdrainage was installed along the buttress backcut and behind the hardface wall, and outlets were provided at the slope face.