drainage behind retaining wall

[jonnyp1]

Hi ive been constructing a deck on a slope and have built a flowerbed in front with deck resting on wall. I put shingle behind wall drainage pipe in geo sock more shingle and more membrane. The wall is about a metre higher than the drainage and the bottom of the slope.There is about a 30 degree slope for couple metres and then more gentle slope to house. During the deluge a couple of weeks ago i came back to find the rain had carried a lot of silt over the shingle and it was slow to drain. I am concerned that over time this will happen more and will further increase silt over drain and may if earth continues to erode affect the concrete supports? Before i put down the membrane and shingle and deck out i wondered if im worrying for nothing or if not any solutions. I assume putting down membrane shingle and the hardwood decking themselves will slow down the flow? Should i dig out all the silt and put more shingle, or fill in the slope with earth making it less steep? Any advice very welcome.

 

[jonnyp1]

any advice most welcome

 

[accelerator]

Adding some pics would help people see what you are talking about.

A diagram of the works would also help.

 

[jonnyp1]

thanks ill put some up

 

[jonnyp1]

heres some pictures.

 

[accelerator]

I'll be honest I don't find your query that easy to follow.

I can't really see the shingle you are referring to.

Essentially, are you worried that the soil around the rectangular concrete block supports in the picture is going to get washed away, weaken your supports, and you'll end up with an uneven deck?

 

[jonnyp1]

Thanks. i put shingle behind the wall laid perforated drain on it and covered in shingle. We had a complete deluge here and silt from the hill ran down and covered pea gravel. So my concerns were yes would it continue to erode down slope even when i put membrane and decking down, if so what are the implications for the supports and my drainage which maybe well be under a considerable amount of silt (lot clay), my main concern being a damp environment under deck which might help distort balau boards?
My latest thought was maybe i should try and make a new drain height where the level is now, lay some dpm and lay a new perforated drain in membrane on that cover in pea gravel and put lots of old bricks i have between that and the slope to try and stop slipage. Or, im going to put a row of posts between the wall and concrete piles with under beam to provide extra support, maybe i could put a barrier between the posts that would stop the errosion? Or am i just over thinking it, it didnt want to lay deck and then problems.

 

[accelerator]

Just to clarify, is the decking coming right out onto the wall that you've built on the left of the photos? So it's a pretty big deck?

So, have you put the drainage in to the right of the wall, at the bottom of the slope? To the right of the black plastic covered wall that can be seen in the photo? At the foot of the wall is where it has all got covered in silt?

Beneath all the decking, what will you be doing with the ground? Will you be covering it with a membrane?

 

[jonnyp1]

yes to all. With lots of broken slab and shingle on membrane

 

[accelerator]

My view - if you are covering the ground beneath the decking with a membrane, then the water should run straight off the membrane and into the drainage, and you won't get the silt, because that is coming from the exposed earth.

 

[jonnyp1]

Cheers

 

[jonnyp1]

Sorry I was going to put damp course membrane under pipe but weed membrane over slope,would water run over aswell as through garden membrane or should I put plastic sheet over lot?