Do I need a Drain behind my retaining wall?

Question

We just had the wall built by friends, who insist that we do not need a drain behind the wall, he left a 11/2 ft margin from the wall to the hillside so the water will drain that way...he says, but the fact is my yard is still flooding!!! everytime it rains half my yard turns into a swimming pool. To be fair we do have clay dirt which I know does not drain very well, and should have been better prepared when the grass seed was planted (which is destroyed by the way) and needs to be sodded now. I'm frustrated because everything I'm reading on the internet states that a drain needs to be placed behind the wall but he insists this would be a waste of money and and that I do not need one. He is telling me that my yard is flooding because the dirt settled in that area and is now lower than the rest of the yard and is sloped now and the water is settleing there now, which I might believe if this wasn't almost right in front of the wall ( 3 ft maybe) can anyone give some advice?

Answer 1

The purpose of a "retaining wall" is to retain in position the weight placed behind it, and as there is nothing behind the new wall, it cannot be a retaining wall., so it does not need a drain behind it. The purpose of putting a drain behind a wall is to allow the water to seep into the ground quicker, to prevent the wall becoming saturated. What I have seen done in these situations is a drain installed right accross the area which gets flooded, at the end of which you put in a Gulley. Plumb the gulley into the nearest surface water drain, now when the suface water races to the bottom of your yard the drain will collect it and take it away. A drainage system is the only way to resolve flooding where you have clay subsoil. A french drain would be ideal, but it must have somewhere to dispose of the water, ie a ditch, or larger drain .

Answer 2

A drain is normally placed behind a retaining wall to relieve hydrostatic pressure in the soil being retained. Since there is a gap between the wall and the hillside, any water in the soil will drain to the foot of the hillside and on the outside of the wall, relative to your property. But, there needs to be some way for that water to drain away, otherwise it will just pond behind the wall, and if the land on your side is a little be lower near the wall,as the level outside rises,the watertable rises inside you land and you have a pond instead of lawn ! So, the upshot of all this is  you need to drain the water that accumulated behind the wall well away from your property  to a drainage ditch or stream. You can do this either by digging an open ditch or installing a plastic or clay drain - your choice.  You will need to cover the drainpipe with gravel or shingle - to allow drainage into the pipe but prevent soil especially clay from blocking the drainage holes. A cheap alternative if it is obtainable is crushed concrete or brick rubble. One other point is that over time, you can expect the gap between the hillside and the wall to fill in, just how much time I cannot say, it depends on how easily the soil surface is eroded by rainfall.

Best of luck.

Answer 3

clay!  that's the problem.  the wall is probably okay if it was constructed properly.  consider building your yard UP with at least 6 inches of top soil & compost before planting anything.  follow the natural lay of the land and consider landscaping using a dry riverbed in the slope.  your yard will become more original this way.

Answer 4

Hi........I've been a carpenter all my life...........and for what it's worth ........you should have a weep pipe and gravel behind every wall.......we even put gravel behind rock walls so that the pressure doesn't damage the wall......it won't happen right away........but in time it's very possible. The water will come to the wall on the surface and drain down the wall to the footings........that's where the pipe and gravel need to be. you only need enough gravel to cover the pipe......probably 9" deep and a 4"line full length of the wall. Find someone with a transit(level) and shoot the elevations of the soil around your house. The soil(dirt) should slope away on all 4 sides of the house........yes I know that's not always possibe so what we do is slope the dirt away and create a valley where the water can get to a storm sewer or street or away from your yard. I always tell young carpenters...to set the elevation of a house so it drains..........some never understand ......but it so important.........Look at mountains .......what do they have.......ya.......creeks rivers and oceans...........so all the best ...if you need more email me.    Also if your yard does have a low spot....put in cheap distribution box with grate and drain the water away, to a safe sight.......where I live we had 12" of rain this year in 36hrs.........I was very thankful that my house was up........because neighbors had their garages and yards full of water.......our city sewers could not handle the flash floor ....too much too fast.......so take care of "yourself" in case something happens.......that your not flooded....bye