Yes get it perfectly. It is a detail full of defects.
The correct detail.
Type one stone compacted for sub-base, Concrete ground bearing slab, Vapour Control Layer, Insulation and then screed (all constructed in the sequence highlighted in my previous post)
Pros & Cons
Pros
1. Regardless of how saturated the ground bearing slab becomes it will alway be below the Vapour Control Layer.
2. The insulation and screed are both installed when the building is watertight with a separating layer between the two to ensure moisture form the screed does not penetrate the insulation.
3. Because you are only installing a lightweight insulation on top of the VCL the risk of damage is little to none, if damage is cause you can see it.
4. Because the screed is laid in the dry and above the VCL & seperating layer its drying period is minimal as you are only waiting for the screed to dry.
Cons
None
The wrong construction detail
Sand Blinding, Vapour Control layer, Mass concrete oversite, screed.
Pros & Cons
Pros
None
Cons
1. Congratulations you have created the perfect environment for a swimming pool.
2. The Vapour Control Layer is susceptible to damage on placing concrete, of course you will never know.
2. The mass concrete oversite (subject to the weather conditions) can / in the case of the OP, become saturated full thickness and of course will be now sat within your swimming pool.
3. Once your building is watertight and the screed is laid, you know have to wait for the swimming pool, mass concrete slab & screed to dry out which I guarantee will be so in time for you install you floor finished. Who wants that amount of water below their floor.
Perhaps one person could justify the use of the above construction detail when we have more robust details.
