Grigoriev's amazing pawn endings (1)

I did not know until I peeked in Wikipedia that Nikolai Grigoriev won the Moscow championship four times.  He's best remembered today as a composer of endgame studies: pawn endings were his specialty.

(After my last tournament outing, I feel that I need a refresher course in pawn endings: maybe you can help me!)

Grigoriev

Shakmatny listok, 1931

White to play and draw

Every pawn ending starts as something other than a pawn ending: it's fairly obvious that White is going to have to give up the rook for Black's b-pawn.  But how?  And how does White draw the pawn ending?

Our new friend the trébuchet may make an appearance in one of the variations.

Solutions in a few hours!