What Happened to the Anti-tank mines?

In the early part of the movie we see a soldier laying down a mine field consisting of both antitank and antipersonnel mines in front of the barricade.And yet at the end of the movie the Chinese tank blows up the barricade and goes through without hitting even one of the antitank mines.The soldiers have to knock out the tank with the 75mm recoilless rifle and the bazooka.So what happened to the mines?