That was my answer when a client asked me if a retaining wall was actually doing anything.
Retain - verb 1 continue to have; keep possession of. 2 absorb and continue to hold (a substance). 3 keep in place; hold fixed. ORIGIN Latin retinere - 'hold back'.
Retaining wall - noun a wall that holds back earth or water on one side of it.
Those are my Oxford Dictionary definitions of the two words above.
The retaining wall on the right is 10' high.
It begins at the rear corner of the house, has two corners, and holds back earth to frame a very nice patio outside the rear door. It is made of pressure-treated wood and is properly inclined to hold back weight. It is also anchored here and there with "dead men," which are perpendicular, T-shaped pieces of the same timber, extending 6 or 8' into the soil behind the wall, and which help hold the wall in place.
If it was not there no patio would be possible and the basement door would open to a concrete stair well. While the wall is a bit imposing, I think the patio is much more functional!
So, after asking me if this wall was doing what it is supposed to do, we had a look at it with my thermal camera. The lavender and purple indicate areas cooler than the surrounding wood. This would be where moisture is present. But nothing looked wet on the patio side of the patio. Water was actually retained.
This wall exactly meets the definition Oxford proposed above! So I said, "Yep, it's doing its job!"
My recommendation: retaining walls are integral to the landscape in many yards. Check them out! Make sure they are doing what they are intended to do. If stones or wood or concrete are out of place or cracked, you might have an expert have a look to make sure it's doing the job intended.