Human model moves, but it shouldn't

I’ve made a model of human and animation for it, then imported to Unity3d. When I start game, then it is all nice, but after a few minutes I see, that model moves under the ground. But it must stay on the same place all the time. What is wrong? I copy all keys from the first frame to the last frame

blend file

  1. check if your model has a rigid body if it doesn’t good!
    2.check that your ground has its colder checked
  2. check that has its collider check as well as components
  3. check to see that you animation doesn’t sink into the ground