When a retaining wall starts to lean, bulge or crack, the assumption is usually that the block or stone was not strong enough. It almost never is. The wall is holding back soil, and soil that cannot drain holds water — after rain, after snowmelt, and worst of all through a freeze. Saturated soil weighs far more than dry soil and pushes far harder, and when that water freezes it expands straight into the back of the wall.
So the parts that keep a wall standing are the parts you cannot see once it is finished. A compacted base below the frost line, so the wall is not sitting on ground that heaves. Free-draining backfill — clean crushed stone, not the clay you just dug out — so water has somewhere to go. A perforated drain pipe at the base of that stone, sloped and daylighted, so the water actually leaves instead of pooling. And geogrid tied back into the soil on anything tall enough to need it.
Height matters more than people expect. A low garden wall is a different animal from a wall holding back a driveway or a slope above a house, and the difference is not just more blocks. Past a certain height the load and the drainage requirements change enough that the wall needs to be engineered, not just built well.
The other common failure is what sits on top. Water running off a patio or a lawn straight over the wall face will undercut it from above no matter how good the drainage behind is. Grading the ground so surface water goes somewhere else is part of building the wall, not a separate job.
Have a wall that is starting to move, or a slope that needs holding? Call God's Gift Masonry at (914) 996-5344 and we will come and look at it.
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