Mesh splitting problem

Hello to everyone.
I am making mesh arrangements for a large terrain. the model consists of a mesh. I open this mesh with rhino and export it in dxf 2004 format without doing anything, and the whole mesh is split into 4-5 pieces. how can i fix it.

Hello - try Weld on the mesh, at 180 degrees before export. If that does not sort it out, please post the mesh file or send to if it cannot be public.