After resuming drilling in Seattle — and only going four feet — Bertha has been stopped again.

After resuming drilling in Seattle — and only going four feet — Bertha has been stopped again.

High temperatures near the machine’s cutting face prompted contractors to stop mining after the drill advanced a total of 4 feet in test runs Tuesday and Wednesday. And that ended Bertha’s attempt to resume mining after an eight-week layoff.

The earlier stoppage remains unexplained. They found some concrete chunks and steel pipe sections in the way, but nothing that could have explained why the drill was blocked. Now the high temperatures pose a more significant problem, as they suggest there is something technical wrong with the giant drill.

Under Seattle Bertha has stopped drilling because something is in the way.

Under Seattle Bertha has stopped drilling because something is in the way.

Something unknown, engineers say — and all the more intriguing to many residents for being unknown — has blocked the progress of the biggest-diameter tunnel-boring machine in use on the planet, a high-tech, largely automated wonder called Bertha. At five stories high with a crew of 20, the cigar-shaped behemoth was grinding away underground on a two-mile-long, $3.1 billion highway tunnel under the city’s waterfront on Dec. 6 when it encountered something in its path that managers still simply refer to as “the object.”

The object’s composition and provenance remain unknown almost two weeks after first contact because in a state-of-the-art tunneling machine, as it turns out, you can’t exactly poke your head out the window and look.