It would appear the building work for the new Euston station has been mothballed. Work has ceased at Old oak common, the last stop before reaching Euston {due to funding problems, big surprise} so they are not sure if it will continue.
So in readiness, should it re start, they are planning to "bury" two huge boring machines at O.o.k. ready to go into action straight away if or when necessary. This pause could be anything up to two years or then again not at all.