VBoxManage convertfromraw imagefile.dd vmdkname.vmdk --format VMDK
Creating the image-file:
sudo dd if=/dev/sda1 of=imagefile.dd
In short:
sudo VBoxManage internalcommands createrawvmdk -filename /mount/mydisk.vmdk -rawdisk /dev/sdc
sudo virtualbox
The long Version:
https://superuser.com/questions/495025/use-physical-harddisk-in-virtual-box#756731