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

• run VirtualBox as root:

   sudo virtualbox 

• link your existing virtual machine or create a new virtual machine with that virtual disk
• set medium attribute to writethrough (File → Virtual Media Manager → mydisk.vmdk)

The long Version:
https://superuser.com/questions/495025/use-physical-harddisk-in-virtual-box#756731