New Retaining Wall Clarifying Questions
Long-time lurker, but this is my first post. I am mid-project in a DIY yard project. I have subbed out a large retaining wall to a civil / wall contractor. It’s 220 feet long, between 2-5′ in height, and makes 2 90-degree turns. It’s built to code with CMU blocks and has an overkill of rebar in it and through the 26″ wide and 14″ deep footer. i’m in Southern California, so it’s a dry climate. I plan to have the face of the wall stuccoed.
The wall just went up this weekend, but hasn’t been filled with concrete, yet. That is coming this weekend. Before he comes back on Saturday morning I wanted to get a few things cleared up for my own knowledge and to know what to ask for to make this wall last. The wall has a lot of room behind it now, but will be backfilled with 12″ of 3/4 gravel and then compacted and graded soil. No landscape fabric.
When reading on the Internet, the topic of sealing the back, “positive” side of the wall has come up quite a few times. People on the Internet say both you should *NEVER* seal a retaining wall and others say you should *ALWAYS* seal a retaining wall. The never crowd says that hydrostatic pressure will build behind the waterproofing and lead to a wall failure. The always crowd says that letting water into the blocks will lead to the blocks deteriorating and the stucco peeling off of the front face in a few years. Some places even seem to have local building codes that either require it or require you not to do it. My local building code does not even mention sealing the backside of retaining walls either way. What is reality – should you seal the back like a below-ground foundation or not seal it at all?
Secondly, my contractor brought in 4″ corrugated pipe with holes on all sides to act as the drain tile at the base of the backside of the wall. I don’t see sock material. I was under the impression that you only wanted the holes on top of a strong PVC pipe so water could easily enter the pipe, but then the continuous bottom of the pipe could run the water out to drainage holes. Is it OK for him to use the pipe with holes on all sides or will the water just go in the pipe and run through it and sit below it?
Thanks in advance for your help!
Replies
First of all we live in SoCal, so unless you live in a flood plain or mudslide area you are not going to get a lot of water staying behind the wall. Unless you have clay soil most of the water is going to percolate to the aquafier pretty quickly. The stucco on retaining walls that I've seen in SoCal only have a problem with over irrigation at the base of the wall where the water wicks up into the stucco. In other words don't sod right up to the base of the retaining wall. Hope that helps
Thanks. The wall faces the sidewalk, so no sod or irrigation concerns there. I'm just concerned with seepage through the wall making the dry-side stucco peel, but you're saying that's not really a concern?
The biggest concern is soil, is it clay or sandy loam? Clay is the problem as it retains moisture. Sand lets water drain to aquafer.
It's not really either. It's mostly topsoil. We're on top of a hill and about 2'-4' down is sandstone and granite. I believe they trucked in the soil when the house was built 70 years ago. It took an excavator and 2 jackhammers 2 days to clear the footer.
was this engineered? 26" footing for a 5' wall seems awfully narrow on anything I've built (needs to be wider to resist overturning and lateral pressure). But maryland soil/fill and CA soil/fill may be different on this score...
Yes, it's from the city's pre-approved plans. Only 12' of the wall is taller than 3'. The footer is wider with more rebar when it transitions to taller than 3'.