How to make a Tall Retaining Wall


Recently, as in September [Final close date was 11/13/2015] this year, I bought a house. This house is on an extreme incline. I would like to level out this incline.

The front first floor of the house sits level with the ground. The property is 120' long and 40' wide. The rear of the property is ~23' below the front of the property. I want to build a wall at the edges while filling the inside until it is level to the front.

I know I have to offset the walls, but what I want to know is with a max of 25' walls slowly turning into level, how much property will I loose. Basically, how much do I offset the walls. I plan to compact the earth as I go along and the project will take place over a few years to help settle the dirt. The final result should be a trapezoid from over head.

In all honesty I considered asking this in Mathematics and Physics since I'm not sure this is reasonably doable. The bricks I'm using are mostly the red ones used to build houses I think 3-5/8" x 2-1/4" x 8". The dirt is fill dirt that I'll be collecting from other sites.

I've done some very basic research, but most of it assumes the wall is a max of six feet.

Edit: I agree with the answers and comments provided. I'm thinking about just building a large porch instead. My main concern regarding the hill is that once I clear the brush away, the hill would erode. Maybe I could use several small walls to make a sort of giant steps?

Update: I did a survey of the area and found that it is kind of a giant hole. Like some huge machine cut the valley out. The walls on the other side are more sheer than my side. It also looks like there was a wall near the bottom of my side of the hill but it gave out maybe 10 years or more ago. The underbrush isn't exactly retaining soil either. I think even grass would be a step up. I'm going to start cleaning the area up after the next hard frost since mosquitoes are still around the area despite one frost. I need a hardy non-invasive plant that will spread out once planted to hold the soil.

Edit2: (Wish I could add comments) If I could get the city to raise two sewer caps or even let me raise them, I could fill in the valley. I'd need about 20,000 cubic yards of dirt. I can get the dirt [shipping would be expensive], but the city won't even let me fix a side walk out front so, it's a no-go.

Best Answer

Building 23' of retaining walls is not a small task. This is a giant undertaking. So be forewarned. :)

As stormy noted, 4' is typically the height you can go without having to trigger an engineering sign-off. However, some areas may also have a total height requirement as well. Personally, if I was buying a house with 6 levels of 4' retaining walls, I'd want to see an engineers signature before making an offer. That's a lot of land that's being held back.

As for how far you need to step back, the minimum is the height of the wall. So a 4' high wall would need 4' of space between it and the next 4' wall. More would be better.