As with the concrete footings, the pool shell can't sit on bare earth.
Popular base materials include sand, small screenings (i.e. gravel), and crusher dust. We're using the latter. Crusher dust is crushed rock with a maximum size of 5mm (~1/5 inch). It's fine, somewhat sand-like in texture, and like road base, compacts well to provide a hard, even surface.
A typical fibreglass pool base is around 100mm (~4 inches). As we have slightly reactive clay under the pool, the engineer has specified 200mm. Given the size of the pool, that's quite a lot of crusher dust - my original estimate was 9 cubic meters, but it turned out to be close to 10 (~13 cubic yards, ~550 buckets, or ~42,000 cups).
With the pool site a good 70 meters (~230 feet) from where the crusher dust would be delivered, I made the wise decision to rent a mini bobcat to move it:
Many round trips later (including one stuck-in-mud event, one broken-fence event, and a few heart-racing moments), We'd moved all of the crusher dust down to the pool site. Unfortunately it still required hand shoveling to distribute it across the base.
Noone wants a crooked pool
The pool shell is 9.3 meters long at the top and 8.2 meters long on the floor. The depth varies from 1.2 meters at the shallow end to 1.8 meters at the deep end. The base we are preparing needs to match this precisely. Any variation from this will show up at the top of the pool, which won't be level. Furthermore since the top of the pool needs to match the level of the various retaining walls, the absolute elevation, not only the slope is very important.
To achieve the correct slope and elevation, I used my trusty laser level to setup two 50mm pipes as screed rails. Once these rails were set to the correct slope and height, I could then screed crusher dust to produce an accurate surface, compact, screed again, compact, and so on. The image below shows the almost complete result while the rails were still in:
Because we will be lifting the pool shell over the house and directly onto the base, I won't have much of a chance to re-lift and fix the base if there are problems. As such, I spent a lot of time ensuring the levels were correct. Let's hope it matches the shell.