I have had a really bad drainage problem in my 46m2 lawn and so have just installed a herringbone style drainage system. I have used 25m of drainage pipe and 4 tonne of pea gravel, leading into a 3ft deep soakaway. What I am unsure about is whether I should be adding sand, or topsoil, to the existing soil, to aid drainage. The ground has been 'teethed' with a digger, and I have then forked, and hoed the ground, I am just a bit concerned that when I then compact the ground, prior to laying the turf, it will form a barrier, preventing the rainwater getting to the drainage! Should I be adding anything further to the soil or should it be OK?!