""""""""""""it's the ground that I don't know how to make from 2D curves""""""""""""

It appears you would have to manually read the contour data contained in the file. Unrealistic. If the terrain contour data was 3d, there are programs that can create the terrain from those. Also, the dxf may have come from some type of engineering package that contains the "real data", but they just sent you 2d?

Can you attach a KMZ file of where this is?

Maybe I can make you a terrain if I can figure out where this is located. Although, uber detail doesnt transfer from poly's to NURBS very well, but maybe having that to reference, then a good poly terrain to combine it with later will be good for you?