Liquefaction and Landslide Hazards in the City of Seattle Luke Gmazel Ryan Thody Kyle Twitchell Jenny VanCalcar Richard Weiner

Our Objective We have been hired by the City of Seattle to determine which landmarks are susceptible to damage due to soil liquefaction or landslides as the result of an earthquake.

What is Liquefaction? Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. When liquefaction occurs, the strength of the soil decreases and, the ability of a soil deposit to support foundations for buildings and bridges is reduced. (source:http://www.ce.washington.edu/~liquefaction/html/what/what1.html)

Liquefaction in Action!

What are Landslides? A landslide, by definition, is a movement of a mass of rock, earth, or debris down a slope. Earthquakes and heavy rainfall are the main triggers for landslides

The Landslide Slide

City of Seattle Aerial Photograph

What is Classified as a Landmark? We found the contact information for the creator of the landmark layer in the Metadata. We contacted Ken Mar, the steward, and asked him what the criteria was for a structure to be classified as a landmark. He informed us that they were chosen by the Landmark Preservation Board and adopted by the City Council.

How could Liquefaction and Land Slides affect the Seattle region? There are 26 landmarks in or within 100 feet of liquefaction zones. There are 16 landmarks in or within 100 feet of landslide zones. In total, 42 historic landmarks lie in or within susceptible zones.

Suggested Liquefaction Improvements Need to improve vertical support beneath structure. This can be done by: Injecting a cementitious or chemical grout Installing micro-piles to the foundation

Suggested Landslide Improvements Need to improve horizontal support beneath structure. This can be done by: Constructing many different types of retaining structures such as soldier piles or “tie-downs” Injecting a cementitious or chemical grout

Conclusion We suggest that the city review the importance of the 42 susceptible landmarks and conduct an in-depth geotechnical evaluation at select sites.