The only way you can import as a mesh is to have the surveyors raw XYZ data file.
Then you can use the "Place Mesh From Surveyor's Data" command.
I am not sure if the XYZ co-ordinates can be extracted from the DWG file.
I vaguely remember something about this from a long time ago - but it may have been a DXF file.
I find it is actually easier to create a mesh using the DWG as a guide for placing splines to create the contours.
The result from a data file probably won't be exactly what you want anyway.
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