Why would the Pennsylvania Railroad fill in a valley and then never finish its plans to develop it . ?

Back when I was very young in early 60's the Pennsylvania Railroad  took over its right of way along its single  track in the Lincoln Lemington Neighborhood of Pittsburgh along the Washington Boulevard Corridor. One day you could walk out my grandfathers back door go down several sets of steps past his and other neihbors gardens they built into the slopes  and go deep down into the woods where the railroad tracks where . The next time we visited the whole valley had been filled in with landfill dirt and rock nearly a half million cubic feet of fill  from Lincoln Ave to clear past Dean street. But why, supposedly the railroad was going to build a new yard for train operations but they already had plenty of such places along its path and the train tracks that ran thru the area saw 1 or 2 trains a week.It actually sees more train traffic now that Box Car Express runs the line.

Of course if you look at the area today you would have no idea the valley even existed now that trees have grown all over it. Since the neighborhood has gentrified and most people who knew about this happening are now long gone  from area or are  dead ,
 The Big question is what was the railroad doing in the first place?
Where they trying to hide something? Did they have all these many truck loads of dirt from some other project and decided to make up a story of development to get rid of it?. also likely becsuse the old east Liberty station was torn down around that time had to be put some where.

I have looked thru many records from the time and can not even find where they ever even applied with the city to even have permission to dump it in the first place. and at this point any one who knew anything about why it was done are long gone, as is the Pennsylvania Railroad which became Conrail  after its bankruptcy in late 60s and eventually transitioned and was purchased and now operates as Norfolk Southern.
There where articles which ran in local papers at time that talked about it  but I have not been able to locate them as yet in the post gazette archives.
I will keep you posted if I find any additional information on this mystery.