The old timber-supported seawall protected Seattle for more than 70 years, but time and a harsh marine environment weakened the structure. Cracks within the wall allow salt water and gribbles – tiny marine borers – to infiltrate and eat away at the estimated 20,000 old growth timber piles that supported the old seawall.
The new seawall is using jet grout to provide a more solid foundation and support for the new structure.
Once excavation is complete, a grout mixture is injected into the ground and mixed with existing soil to create columns of stabilized soil.
Wood platforms are used to provide stability for the jet grout rigs as they travel through the work zone.
A mixture of water, grout and air is injected at high pressure into the ground to form over 6,000 five-foot columns in a honeycomb pattern along the project area.
Though the grout mixture can be messy at times, it is an essential piece of the seawall structure. Jet grout columns will entomb the old seawall support structure, providing the foundation for the new seawall and reducing the seismic risk of liquefaction.
For more information about the Seawall Project, visit our website.