Our builder was very concerned about wall collapse because our soil is so poor. In fact, a moulded bench did collapse after rebar was in place and we had to pay an additional $800 for workers to manually clear all the dirt. There was only about 3 days between the rebar completion and the shoot.

You need to be sure all that loose dirt is removed which will mean more concrete usage (more $) and thicker walls. Our walls ended up being about 12-14" thick so I would say there was 3-4" of spacing between the rebar and the dirt.

~Rick~