In PLAXIS 3D, I could see the flow movement if I don´t have any groundwater or phreatic level and only I have a head in a dam?
A Head groundwater flow boundary condition defines a water level along the boundary this is applied. Therefore, you should expect to have a generated pore pressure distribution according to the head value defined.
Please check our Reference manual for more information concerning groundwater flow boundary conditions.
A nice example to follow is our tutorial #7 of a Rapid drawdown analysls:communities.bentley.com/.../plaxis-3d-tutorial-07-rapid-drawdown-analysis