The Marina del Rey Seawall was constructed during the late 1950's and early 1960's as a means of  reclaiming a low lying swamp area for dry land uses.  The original construction was high quality for the time, as evidenced by its 30 plus years of service life to date.  In February 1986, a failure mechanism that resulted from severe corrosion of the vertical reinforcement occurred when an isolated 60 foot wall panel collapsed.  An engineering investigation into the collapse concluded that the failure was caused by corrosion of the reinforcing steel due to exposure to natural seawater.  No other factors were identified as having contributed to the collapse. The vertical flexural reinforcement in the cantilevered wall had been subjected to aggressive saltwater exposure principally through a construction joint located near the base of the wall.  The long-term exposure to seawater has led to chloride-induced corrosion of the reinforcing steel crossing the construction joint, and attendant concrete deterioration on the hidden (land) side of the wall.  Because of the non-redundant nature of the cantilever wall system, loss of primary vertical reinforcement at the wall base by corrosion results in a loss of overall structural integrity.

A restoration program with three (3) distinct focuses was developed by the Los Angeles County Department of Beaches and Harbors (LADBH) and the Department of Public Works (LADPW).  Program focuses were:

1.  Utilize an impressed current cathodic protection system to mitigate active corrosion of the seawall reinforcing steel.

2.  Utilize a drilled caisson “strong-back” system to reduce reliance on the vertical reinforcing steel which has been subjected to corrosion and to upgrade the seismic behavior of the system.  The “strong-back” concept was developed by the LADPW and was successfully installed in a trial repair in the Marina.

3.  Conduct nondestructive impact-echo testing to locate corrosion damage.  This allowed for categorization of repairs based upon extent of delamination and concerns for life-safety in areas of high public exposure.

Initially (1994), WDP was retained to provide a peer review of impact-echo testing conducted by another firm on 40 random panels of an approximately 7.5 mile seawall.  After completion of the peer review, WDP conducted its own limited testing to demonstrate the veracity of the method to locate unseen corrosion damage in the retaining wall.  Several theoretical models for the corrosion damage were developed by WDP.  Core testing independently verified the accuracy of the hypothesized damage modes and testing by WDP.

In 1995, WDP was retained as the Structural Engineer-of-Record for the project.  A database management system was developed to be used to assess changes in the integrity of the seawall in the future.  WDP designed the tie-back system to strengthen the wall based on corrosion damage and seismic considerations. By conducting the impact-echo testing and tailoring the repairs based on damage detected, WDP was able to save Los Angeles County about $5.8 million in construction cost.

Services WDP used on this project included:

• Structural Analysis
• Conducted Life-Cycle Cost Analysis
• Nondestructive Testing
• Development of Corrosion-Damage Models
• Geotechnical Investigation
• Liquefaction Risk Analysis
• Seismic Analysis
• Repair and Seismic Upgrade Design
• Preparation of Contract Structural Drawings and Specifications