The 6 top causes of retaining wall failure.
Retaining walls can fail for any number of reasons, some more common than others. Usually when a wall fails there is more than one thing wrong with the wall. One thing that all failed walls have in common is that the failure was avoidable.
1. Drainage not installed correctly – or at all - as we will see is sometimes the case.
Walls must be drained, if they are not you will have a problem. Depending on the season, amount of water and wall material the wall fail in different ways. Bt the point here folks is that the wall will fail.
Notice how this wall had no gravel behind it or around the drainige pipe
2. Soil not reinforced.
Geogrid is used to reinforce soil, forget to use it and all bets are off.
Check out how strong Geogrid is in this video below.
3. Base not correctly installed.
Base must be installed correctly. A wall cannot be balanced on a pad of gravel the same with as the wall material. At a minimum the base must be 3 times as wide as the first block and set deep enough to bury one block.
4. Rebar not correctly installed in concrete walls.
When building a concrete retaining wall rebar must be used correctly. The corners are especially tricky, I tried looking online for a picture of the correct way and only found one.
Here it is.All the others looked like the picture below which is wrong.
Below is what happens if you do it wrong. The wall is only 4 months old! In this photo the rebar is too few and not in the correct position.
5. Block walls not installed correctly (you truly won’t believe this!)
Believe it or not there are contractors out there that build retaining walls upside down. A lot of them! It’s just stupid, but it happens. Here’s a picture of a retaining wall where the block is upside down, no drainage to speak of, no soil reinforcement, base too high etc etc…
This wall shown here was built upside down. The slots should be facing up and the holes fasing down.
6. Some retaining walls need an engineer.
Don’t try and save money here. If your wall needs to be engineered hire one, preferably that specializes in walls. See, when an engineered wall fails it’s comes down to one of two things. Either the contractor did not follow the engineers plans or the engineers plans were bad.
In closing, retaining walls are projects that demand to be built correctly. Trying to save money on a wall is false economy. You will pay much more in the end if a wall fails.
I was motivated to write this article because of a story I had been told about a year ago that still sits in the back of my mind. I went to a retaining wall seminar at the New England Grows trade show. We learned all sorts of things about retaining walls that are only interesting to people like me that build them. The Speaker - Vern Dueck – has built more walls than probably anyone in I know of. He actually holds the patent for the Cornerstone wall system.
At the end of his seminar he told us about a friend of a friend that had asked about building a retaining wall. Vern told the guy based on his description of the project an engineer was required. Well people being people and trying to save money he decided to build the wall himself – without the help of an engineer. That guy did have help though, his wife and a plumber friend that had a small excavator to help dig. Nearing the end of the project the wall fell and killed his wife. The wall fell extremely fast, he was talking to her when it happened. This was 100% preventable.Not every wall needs an engineer and truthfully most of the walls I build don’t. They are simply not tall or complicated enough. But when a retaining wall professional says the wall needs an engineer he’s not saying this to make his engineer friend rich. He’s telling you this because your project is not an off the shelf cookie cutter type of job. Besides a good engineer will save you money. You won’t over or under build it. Over building costs more because of materials, under building costs more because you do it twice or worse someone gets hurt.