Q&A: What were the challenges of the Crescent City Harbor Rehabilitation Project?

Crescent City Inner Harbor

Floating docks and piles were replaced with stronger concrete versions.

A little background information

Four years ago the Crescent City Harbor, named for the crescent shaped beach south of the city, was destroyed by devastating tsunami waves generated from an 8.9 magnitude earthquake in Japan. Langan provided geotechnical engineering services during design, contractor selection, and construction for the rehabilitation of the harbor. The harbor previously consisted of floating docks, which served as slips for commercial and recreational boats, supported by concrete piles with relatively little embedment into the weak bedrock. Most of the concrete piles were sheared off by the forces generated by the tsunami waves. The project included replacing the old piles with piles designed to resist future tsunamis, stabilization of the harbor slopes, and other onshore improvements.

IMG_20130925_104248_554-retouch-LM

New foundations were constructed for the three gangway landings.

Challenges

Langan was a critical part of the project team, working closely with Ben C. Gerwick and Strover Engineering, from 2011 to 2014.  The challenges of this project included designing the facility to resist future tsunamis, shallow highly-fractured bedrock, and high seismicity and potential for strong ground shaking.

Langan’s geotechnical engineering services included developing lateral pile response analyses (L-Pile) to aid in the design of the floating boat docks, providing recommendations and design criteria for the foundations of the gangway landings, and reviewing contractor value engineering, testing, and installation logs. The lateral capacity of the piles included kinematic forces due to a design level tsunami.  In addition to foundation design, we also evaluated the stability of harbor slopes for both static and seismic conditions, and provided recommendations for increasing their stability. We used historical design documents and boring longs, as well as the result of our exploration on land and water.

Crescent City Inner Harbor

A barge-mounted drill rig was used to advance the borings over water.


Today, Crescent City Harbor is completely restored and fully operational. Overall, Langan’s engineering design services were a critical part of assisting the Harbor District in achieving their goal to recreate the harbor better than it was, with the ability to withstand future natural disasters.

 

Answer provided by Haze Rodgers, PE, GE
Haze has over twelve years of professional experience managing, developing, and performing geotechnical studies including explorations, analyses, and construction observation services for various projects throughout California, specializing in offshore design.

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