entrenching battalions

[manxman]

As usual my query has a Liverpool Scottish slant

I have been able to establish that my Great Grandfather was sent to France from the Liverpool Scottish depot/ 3/10th battalion in June 1917 and was subsequently sent from an unidentified entrenching battalion to the 1/10th sometime in August 1917.

Does any one have any ideas as to which entrenching battalion would have supplied drafts to the 1/10th Liverpool Scottish in August 1917? (the battalion's war diary shows that there were three reinforcing drafts in August '17), or indeed the 55th West Lancs Division as a whole?

Would the troops sent from a regimental depot always be routed via a particular Infantry base depot (IBD) in France before being sent to a particular entrenching battalion?

How many IBDs were there?

any info gratefully received