Preparing sub-grade - Backfilling trench with 110 waste pipe

[JJBB123]

Hi, I am new here.

Now that I have had time on my hands, I have decided to start work in my garden for a new porcelain patio.

I have removed between 240-300mm of top soil from the whole garden and dug deeper into the sub-grade to make a trench for a waste pipe for a linear drain at the end of my patio. I have also gone further down into the sub-grade around the man hole to connect the new waste pipe using a rotavator. My sub-grade is not at the same levels/falls as the planned patio and is bumpy.

1. I have put pea gravel around the new waste pipe, what is best to back fill the rest of the trench? Can I use the sub-grade I have removed or best to use more gravel?

2. Does my sub-grade have to have the same level/falls as the patio? If it does, can I back fill with the removed sub-grade and use a Wacker plate before adding the mot type 1 sub base (4 inches)? or just add more type 1 to the lower levels of the sub grade?

Your advice would be much appreciated.

Thanks

[Tony McC]

1 - backfill with gravel around any pipework, and ten use typw 1 when clear by 100mm or more

2 - not nesser celery. The sub-grade should be cleared of any organic material and soil and the final profile is unimportant. It's the *sub-base* that has to match the eventual profile of the planned patio, even if that means the sub-base is, say, 100mm deep at one point and 200mm elsewhere.

[JJBB123]

Many thanks for your advise.

[JJBB123]

When would it be best to fit the channel drain that will go in-between my porcelain patio and astro turf? The sub-grade is lower for the patio.

After some reading it looks like it's best to install the drain to the sub-grade then put type 1 either side. Is this correct?

Thanks again