Seattle’s State Route 99 boring machine* (Bertha) ran into trouble while boring through sloppy old tide flat dirt and fill material. Some of the water and abrasive material made it past the seals designed to keep it out and into critical bearings for the cutters on the head of the boring machine, causing it to overheat. So a big hole had to be dug to get to the cutter head, lift it out, and repair it. (The stoppage occurred in December 2013, and the project is now some two years behind schedule).
At midday Thursday, the top portion of the SR 99 tunneling machine’s cutterhead broke through the southern wall of the access pit. It will be several months before boring can continue, and there is still a long way to go.
*A tunnel boring machine with a cutting head that is 17.5 m (57 ft) in diameter.