SEATTLE (AP) — As Seattle's tunnel project prepares to bore beneath the Alaskan Way Viaduct, city and state officials are worried about growing sinkhole risks.

The Seattle Times reports that geotechnical expert Gregg Korbin says the giant boring machine called Bertha is over-excavating the area, increasing the likelihood of sinkholes. Korbin is a member of the state's Strategic Technical Advisory Team.

Gov. Jay Inslee ordered contractors at Seattle Tunnel Partners on Jan. 14 to stop drilling until they submitted an analysis of a Jan. 12 sinkhole and provide a plan to improve operations. The project was suspended for six weeks, which STP project manager Chris Dixon says was wrong and unjustified. Bertha resumed digging Feb. 23.

STP's new Tunnel Monitoring Action Plan specifies how much the busy highway that is the viaduct may tilt before work would be stopped.