Monitoring of Dolos Armor Units at Crescent City, California

Abstract : Crescent City breakwater is located on the California coastline approximately 17 miles south of the Oregon border. In 1974 and again in 1986, dolosse were placed along a section of the breakwater particularly susceptible to damage. Monitoring of above water dolosse moment and breakage has been conducted since 1986. In August of 2004, a detailed monitoring survey was conducted of the dolos section of the Crescent City breakwater. The goal of this monitoring is to understand the long-term structural response of the dolosse. Detailed monitoring included ground surveys, aerial photography, photogrammetric analysis, and a broken armor unit survey. Results showed very little dolos movement has occurred since the end of the initial nesting period in 1988. Furthermore, no additional dolos breakage was observed since 1993. From 1995 to 1999, core samples were obtained from dolosse cast in 1986 and in 1974 in order to determine the in-situ strength of units in both non-loaded (near concrete cap) and highly loaded regions (near still water level) of the structure. The cores were subjected to standard laboratory concrete strength tests. Results indicated that the structural strength has increased considerably since construction for non-loaded units. However, concrete strength for units placed in highly loaded units near the still water level was near constant.