You can use the following syntax to install Civil 3D silently. Open the Command Prompt window with administrative privileges and enter the following syntax:
<mediaDriveLetter>\Setup.exe --silent --install_dest "<InstallLocation>"
<mediaDriveLetter> is the drive letter where the media is mounted or the setup.exe file is stored.
<InstallLocation> is an optional customized install location. The default install location is C:\Program Files\Autodesk.