Hello,

I am a newbie to the forum as well as retaining walls and patio slabs. I am currently in the process of putting up a retaining wall to support a patio. The goal is for the patio to take the place of the deck (obviously not height wise). I have place a few coarse of block as well as drainage pipe and 1 inch gravel. Total height of the side picture will be 40" tall.

My question is: What can I fill the whole area with and compact to make the most support for a slab? Size rock? See attachment for photo.

Thanks

 

40" of any compacted material is a lot of mass.

What type of base did you install under the blocks?

 

Exactly what blocks are you using for your wall?

Crushed stone is the one of the easiest base materials to work with. Lay it out in 3-4" thick layers and compact with a plate compactor. Then add your next layer.

The big issue will be how much of the existing soil to excavate. The dirt up next to the house and where you remove the posts is not virgin undisturbed soil. When a house is built they do not compact the soil when they back fill around the foundation. So, depending on how long ago the house was built you may still have settling in those areas. If you were building an addition onto the house they would require your footings to go down to the same depth as the house or have an Engineer certify the compaction of the soil. You'll have to look at your site and see what you think is best.

You can test the compaction by using a 4x4 post, maybe an old one from your deck. Hold it vertically and lift it high and drive it down onto the ground. Do this next to the house in several areas then go out into your yard well away from the house and do it to get an idea for comparison. If the soil next to your house makes a deeper hole or sounds hollow you might consider excavating the loose soil or do some additional compaction before installing your stone.

 

Thank you Marq1. I compacted down to about 10" of crushed stone sand mix.

 

Thank you so much for your reply Pilot Dane. The block has a 6" by 16" face with a 10" depth. Weight of 65lbs.

 

From pictures it looks like the blocks go down hill. Are they level?

 

You may want to consult the manufacturer of those blocks you're using. Many types of block like that are only rated for 2'-3' wall height without making special provisions for additional support. The manufacturer may also be able to provide some good insight into what the best type of fill material would be.

Pilot Dane made a good point about the compaction of your existing soils. A large part of that is dependent on how old your home is. If it's over 10 years old or so the compaction of the existing soil along your home should be sufficient, if the home is newer additional work maybe needed in that area also.

 

Pugsl hit my concern, it looks like the top of the wall is not level.

 

Thank you so much for your concerns. I will check the wall to make sure it's level tomorrow morning when I get off work. I really appreciate everyone's advice. I'll take as much as I can get.

 

While you are in the planning stages, don't forget to install some sort of drainage system to relieve the hydraulic pressure that will be inevitable.

 

Thanks Chandler. I placed a 4 inch perforated corrugated pipe next to the base that feeds out the side I took the picture of. I am going to continue it all the way around.