1018 14TH ST 2023-02-09 - Laserfiche WebLink

Y Port of Everett SHANNON 6WILSON,INC. Attn: Mr. Erik Gerking April 16, 2013 Page 4 of 5 RECOMMENDATIONS If the level of damage described in this letter is not acceptable to the Port,there are several options for improving the seismic performance of the bulkhead. These include: ■ Increase the stiffness and depth of the wall by designing the wall for the IBC design level ground motions. ■ Use tieback anchors or pile-supported deadman anchors such that wall resistance is maintained when the soil liquefies. Per Gazetas et al. (1990), bulkhead movements may be reduced to less than about 6 inches if the anchorage system does not lose support due to soil liquefaction. It should be noted, however,that this may also require structural modifications to the wall to allow for load transfer so the wall structure does not fail. ■ Improve the ground behind the bulkhead such that liquefaction does not occur in front of the deadman anchors. This could be performed by using vibro-compaction or installing stone columns that extend to the bottom of the liquefiable soils (elevation -12 feet). This would also mitigate ground settlement due to liquefaction. If 2 to 8 inches of ground settlement can be tolerated,then earthquake drains could be used to mitigate lateral spreading. Other ground improvement techniques may also be used but are typically more expensive. Based on McCullough and Dickenson (1998), bulkhead movements could be reduced to less than 2 inches if liquefaction is mitigated by improving the ground. If requested by the Port, we can provide recommendations for pile supported deadman aiichors, and/or ground improvement. It should be noted that the empirical analyses discussed in this letter are based on empirical earthquake case histories and do not provide a site-specific estimate of anticipated ground movement. We hope this letter provides the information you need to evaluate the risk that the Port will accept if the bulkhead wall is designed for the 200-year return period ground motion. If you have any questions, please contact me at 206-695-6837 or maa e shanwil.com. Sincerely, SHANNON & WILSON,INC.