Hi @Mpcconsultora ,
the issue can be caused by rounding variance between the two applications Civil 3D and InfraWorks, maybe you are re-projecting data?
However, make sure the terrain data is a bit larger than all other data. Everything in InfraWorks is more or less draped on terrain. If you add an aerial image that is larger than terrain, it's lowered to elevation 0.0 m then, causing such "waterfall effects".
Regards,
Karsten.
Karsten Saenger