Draining a soggy lawn

[Dickdastardly]

I will be installing 60mm perforated land drains in my lawn as soon as things have dried up a bit. I will be following the guide on this site but one thing is niggling me... the geotextile membrane is to be 150mm below the surface with the remaining backfilled with topsoil/turf. I am wondering that when this top soil layer becomes saturated after prolonged periods of rain will it then become impermeable? So my question is would it be an idea to mix the topsoil maybe 50% with grit sand before replacing to aid water to filter down more efficiently. If it wasn't a lawn I would just extend the granular stone to the surface but this isn't an option.

[lutonlagerlout]

plants grass etc need some topsoil to live in
if the drainage works you may be surprised how desiccated the garden gets :;):
cheers LLL

[Tony McC]

You need that 150mm of topsoil to sustain the grass, as LLL rightly says.

If that is *good quality* topsoil, it will be free-draining, so there is no risk of it clogging, no matter how much rain we get. If you wish, you could mix the topsoil 50/50 with grit or grit sand to further improve its permeability, but, to come back to the main point, one of the key properties that makes topsoil "good", is the capacity to be free-draining and for it NOT to retain too much moisture.

[Dickdastardly]

Thanks for the advice. I need to stop over-thinking these things!