Backup image three times larger than original!?
Working with Acronis® True Image Echo Workstation® mit Acronis Universal Restore® (build 8.076) I made an image of an external harddrive (465 GB altogether, 310 GB of free space) to another external drive (465 GB altogether) and the backup on this disk is now 455 GB big! What made the required space explode from 155 to 455 GB? I already used chkdisk but found no problem on both external disks.
Not sure about Workstation but if the option is available to make a sector-by-sector backup is enabled it will make an image of the entire partition, not just the in-use sectors. The other reason this can happen automatically is if TI doesn't understand the filesystem for any reason such as corruption or an unsupported filesystem. Since you ran chkdsk this is unlikely.