Alaskan Way Viaduct keeps sinking

The Alaskan Way Viaduct is still sinking, according to inspection results from the Washington State Department of Transportation, but there’s not believed to be any immediate risk to the public.

Survey crews found the viaduct sank another quarter- to half-inch near the Seneca Street exit, putting it about 3.5 inches lower since the 2001 Nisqually earthquake. Inspectors also noted additional cracking on columns and girders in that general area, along with up to a half-millimeter widening of a few existing cracks. The settlement is described as “uniform in nature.” A WSDOT spokesperson told The Times that the damage isn’t severe enough to require emergency repairs.

Related: Bertha testing underway as Seattle crews race to meet December schedule

While the south portion of the viaduct was demolished in 2012, the part that runs along the Seattle central waterfront is supposed to last until after the new Highway 99 tunnel is completed in early 2018, according to the Times.

The WSDOT website notes that all additional settlement of the viaduct is “significant” and that no single number represents an acceptable level.

“Those limits vary along the length of the viaduct based on ground conditions and the condition of the structure,” WSDOT says. “How the ground settles is also important. A structure that settles uniformly is less likely to be damaged than a structure that settles unevenly.”

The Times reported that the WSDOT spokesperson said it was unclear what caused the damage, but one possibility is repair work done last year to widen an expansion joint.

The Seneca Street ramp is six blocks away from the 120-foot-deep vault where tunnel-boring machine Bertha is being reassembled, The Times reported.