I saw this story yesterday:

http://www.yakimaherald.com/news/yhr/th ... l-drilling

Apparently there is some speculation that they may have hit debris used for fill under an old rail yard, which could include discarded locomotives, or it could be something as mundane as a very large rock. It'll be interesting to see what the object turns out to be.

Jimmy Hofa ??

Somehow I don’t think a buried railcar would stop Bertha the Boring Machine.

According to the Washington State DOT, the boring machine is now below the 100-year-old layer of fill. In other words, it is now in the numerous layers of glacial deposits, meaning that the unidentified obstruction is in all likeliness a large boulder left behind as part of the glacial strata.

This is not the first time a major highway construction project in Seattle has had to deal with glacial deposits.

In the early 1960's, when the first segment of Interstate 5 was being constructed through Seattle, a large deposit of pressurized glacial clay was encountered at the future location of the intersection between I-5 and SR 520 at the base of Capitol Hill. A large retaining wall had to be built to hold back the clay, which is still visible along the offramp from northbound I-5 to eastbound 520.

In the late 1980's, when the third tunnel for Interstate 90 was being bored through Mount Baker Ridge above the west shore of Lake Washington, deposits of semi-liquefied sand and pressurized clay had to be dealt with.