If you expect you will be excavating a lot of brick in the long term, I recommend investing in a digging bar for excavating the unwanted brick etc. There are several styles, but they usually have a blunt chisel digging blade on one end of a 6 foot heavy steel bar, and are blunt at the other end.
I think I'm pretty much clear of bricks (these belonged to the previous tenant, rather than historically present).
Trouble is, the site's a former spoil heap from iron ore mining & when the site was turned into allotments 20 or more years ago, the quarry waste used to seal the spoil was just flattened & insufficient soil put on top (council ripped off by whoever did the work...).
I do indeed have one of those bars in my armoury, along with post hole tongs which will come in handy for setting the polytunnnel anchor plates.
Today's effort saw the top layer of weeds cleared off the rest of the polytunnel area & thankfully, an increase in soil depth, now up around 6-8".
It'll be closer to a foot once I've added the soil from elsewhere.
Plan is to start putting the tunnel up next week by getting the anchor plates & tubes carefully positioned & levelled & the hoops & bars installed.
Getting the cover on, doors installed, etc. on the Sunday/Monday after.
6 ton of topsoil & 3 ton of green waste compost coming later in February.
I really should be taking photo's...