It sounds as though the information in the LandXML is information we do not read into the InRoads/Powercivil product. Since the Civil3D TIN file is triangle based, they store triangle information and can export it to the LandXML. InRoads cannot read these triangles because we are a feature based program. So if the information exported from Civil3D is just the triangles and not the features/points, it will not import into InRoads. Try exporting the data from Civil3D and export the features instead of just the triangle model.
