Hi, folks, I came across this site after a Google search on retaining wall structure - and I need your advice…
I need to build a short wall in front of the house, and I wish to make it last for decades. The height will be about 30 inches and the width about 8-10 inches. It will be made out of stones and mortar, and will be at the edge of a small lawn.
I want to lay the first course about 6 inches below grade, but is it necessary to place crushed rock and a drain pipe at the base of the wall under the fill dirt behind it?
Yes if you want it to last for decades. The crushed gravel acts as a drainage and the drain tile keeps water away from the foundation of the existing retaining wall. It is not the rocks that will degrade it is the mortar.
The gravel must be filled in (6-8" thick) behind the wall as well and the tile should be placed behind and at the bottom of the wall. Landscape fabric should extend from below the tile & gravel and up behind the gravel and then over the top of the gravel to meet the top backside of the wall. This will prevent infiltration of the soil into your gravel backfill. The backfill may stop 4-8" from the top of the wall and topsoil may be filled in to plant grass on. The drain tile should terminate as far away from the wall as possible depending on your setup.
The goal in all of this is to prevent a buildup of moisture behind the wall which will create hydrostatic pressure. When this occurs the wall will inevitably fail by tipping over(most common) or sliding out at the base.
One other note, don’t miss what Kevin said, “crushed gravel” is the proper base and backfill. Under no circumstances should you use pea gravel as many contractors may do.
You may also choose to install weep holes along the front base of the wall to help drain moisture away from behind, but with a drain tile this is not important. This would be done as a backup drainage system in the event your tile should clog or fail completely.
Now, could anyone direct me to early-1920’s style examples? Or, what material could be used for a Central Florida install? The pillars are finished with stucco, and there are no riverbeds anywhere near.
Hopefully Robert V Young chimes in and helps you with this. He does this regularly and may have some pictures of illustrated design stone work. I will say that when I was learning we started with big stones and tappered to the top. No tie back was needed as the structure was built like a peramid. We also designed with secondary weep holes.