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French Drain Depth

Hi Guys,

I'm in the process of sorting some french drains myself. I'm doing them the recommended way, trench lined with a geotextile fabric, perforated drain at the bottom and then filled with stones and wrapped into a burrito. On top of that we will be putting decorative stones.

The width of the trench is 30cm, and we had planned to go 30cm deep. I've begun digging and have found that it becomes significantly harder around 27cm. More so towards the back, thicker clay and rubble pretty shallow (typical new build). Had to pull a paving slab out that was mostly in my garden but buried next door too, luckily only slightly so I didn't cause their garden to collapse!)

I've been reading about it, and there's mixed views on it as always! The main concern when it comes to depth is if turf goes back over and someone was to try and stick a fork in it. Nobody is going to stick a fork in it as it's got stones on top and even if it had turf, it'd hit the stones around the drain first anyway. Also encountered one object at one point that is 10cm deep that I'm pretty sure I won't be able to get out, it looks like an old branch that is significantly running across garden borders into nextdoor. Looks very much like a pipe but I am thinking surely not at 10cm depth.

The drain itself is 110mm wide, so I can use the first 20cm for the drain then 7cm is more than sufficient for the decorative stones, if not a little overkill.

Am I missing anything?
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