What seven years of Seattle viaduct inspections have found

Oct 6, 2017, 9:33 AM | Updated: 11:58 am

(Seattle DOT)

MyNorthwest.com

Ever since the magnitude 6.8 Nisqually earthquake damaged the Alaskan Way Viaduct, the state has conducted twice-yearly inspections of the seismically vulnerable and outdated viaduct.

The quake that struck just before 11 a.m. on Feb. 28, 2001 caused more than $1 billion in damage to buildings and roads.

The Washington State Department of Transportation made $3.5 million in repairs to the viaduct after the quake.

As the city waits for a replacement to the viaduct — in the form of a 1.7-mile tunnel — the state continues to monitor it. Beginning Friday at 11 p.m., the state will close the northbound lanes until 5 a.m. on Monday. Southbound lanes will be closed from 5 a.m. to 6 p.m. on Saturday and Sunday. The closure is between South Spokane Street and the north end of the Battery Street Tunnel.

Viaduct inspection findings since March 2010, according to state

March 2010: Survey crews detect no new settlement or structural damage.
Oct. 2010: Survey crews detect new settlement near Columbia Street. Measurements indicate the structure has settled a half-inch at this location since the previous inspection. No new structural damage is detected.
March 2011: Survey crews detect no new settlement or structural damage.
Oct. 2011: Survey crews detect new settlement near Columbia Street. Measurements indicate the structure has settled 3/16 inch at this location since the previous inspection. No new structural damage is detected.
March 2012: Survey crews detect settlement at two locations: Seneca Street and Yesler Way. Measurements indicate the structure has settled 7/16 inch near Seneca and 3/16 inch near Yesler Way. New cracking is detected near the Seneca Street off-ramp. Crews find no new structural damage.
Oct. 2012: Survey crews detect new settlement near Yesler Way. Measurements indicate the structure has settled 3/16 inch at this location since the previous inspection. New cracking is detected near the Seneca Street off-ramp. Crews detect no new structural damage.
March 2013: Survey crews detect new settlement near Railroad Way South and South Washington Street. Measurements indicate the structure has settled up to 1/4 inch at this location.
Oct. 2013: Survey crews detect new settlement at two locations: Seneca Street and the area between Columbia Street and Yesler Way. Measurements indicate the structure has settled 1/8 inch near Seneca and up to 1/8 inch near Columbia/Yesler since the previous inspection. Crews also note the widening of existing cracks near Seneca. No new structural damage is detected.
March 2014: Survey crews detect new settlement between South Washington and Seneca streets. Measurements indicate the structure has settled up to 1/8 inch at this location since the previous inspection. Additionally, crews detect new cracks and expansion of existing cracks near Seneca Street; additional monitoring equipment is installed in the area.
Oct. 2014: Survey crews detect new settlement at two locations: near Seneca Street, and between South Washington Street and Yesler Way. Measurements indicate the structure has settled 1/16 inch at these locations since the previous inspection. Additionally, crews detect lengthening in an existing crack near Seneca Street. The crack does not require repair. No new structural damage is detected.
March 2015: Survey crews measure 1/8 to 1/4 inch of additional settlement near Seneca Street. Some widening of existing cracks noted. Additionally, crews note two new cracks on columns near Yesler Way. New crack gauges and focused monitoring in these areas. Other crack measurements are stable.
Oct. 2015: Survey crews detect between 1/4 and 1/2 inch of additional settlement between University Street and south of Seneca Street since the last inspection. The settlement is uniform in nature. Inspectors also note some additional cracking on columns and girders in the same general area, along with up to 1/2 millimeter widening of a few existing cracks. No additional repair work is necessary.
March 2016: Survey crews measured approximately 5/16 of an inch of settlement near Seneca Street and between 1/8 and 1/4 inch of settlement at the Columbia Street on-ramp. Crews also observed upward movement of up to 1 inch at some locations at the south end of the structure. This upward movement is uniform in nature. No new cracking or structural damage was found.
Oct. 2016: Survey crews measure up to 7/16 inch of settlement near Seneca Street. No new cracking or structural damage is detected.
March 2017: Survey crews detect up to 1/4 inch of settlement near Seneca Street since the last inspection. They also note that an existing crack near South King Street grew by 2/10 millimeter. No new cracking or structural damage is detected.