4 Reasons Why Your Retaining Wall is Failing (And How to Build One That Lasts)
A well-built retaining wall can transform a sloped, unusable yard into a beautiful, terraced landscape. But here in Minnesota, our notorious "freeze-thaw cycle" puts hardscaping to the ultimate test.
If you’ve noticed your retaining wall starting to lean, bow, or crack, you aren't alone. Failing retaining walls are a common sight in the Twin Cities. But why does this happen, and more importantly, how can you make sure your next wall is built to withstand Minnesota’s harsh elements?
Here are the top reasons why your retaining wall is failing, and what it takes to build one that lasts in our region.
Why Your Retaining Wall is Failing
1. Poor Drainage (The #1 Culprit)
The most common reason retaining walls fail in Minnesota isn’t the block or the stone—it’s water. When water builds up behind a wall, it creates massive hydrostatic pressure. Because much of our local soil contains heavy clay, it traps water rather than letting it drain. When temperatures drop, that trapped water freezes and expands, pushing the wall outward. If your wall lacks a proper drainage system, it’s only a matter of time before frost heave causes it to buckle.
2. An Inadequate Base
A retaining wall is only as strong as its foundation. If a wall was built directly on top of topsoil or an uneven, uncompacted base, it will inevitably settle and shift. In Minnesota, the ground shifts dramatically as it freezes and thaws. Without a deep, highly compacted base of crushed rock, the wall will warp, sag, and eventually collapse.
3. The Wrong Backfill Material
What’s behind the wall is just as important as the wall itself. A common DIY mistake is using the excavated dirt to backfill directly against the back of the blocks. Dirt holds moisture and expands when frozen. Proper retaining walls require a buffer zone of clean, crushed rock immediately behind the wall to allow water to filter down safely.
4. Underestimating the Load
Retaining walls hold back tons of soil. If there is a driveway, a patio, or a steep slope above the wall, it adds "surcharge" (extra weight). Walls that are built too tall without proper reinforcement simply cannot handle the sheer force of the earth pushing against them.
How to Build a Retaining Wall That Lasts in Minnesota
If you are replacing a failed wall or adding a new one to your property, it requires a region-specific approach to survive our climate.
Start with a Proper Trench and Base
To combat frost heave, the foundation trench must be dug deep enough to accommodate a thick layer of crushed, compactable base rock. This base must be perfectly leveled and heavily compacted before the first block is ever laid. Furthermore, the entire first course of blocks should actually be buried beneath the soil line to securely anchor the wall.
Install Superior Drainage
Water needs a way out. A wall built to last will include a perforated drain pipe (often called a French drain) running along the bottom of the trench behind the wall. This pipe catches water and directs it safely away from the wall’s structure before it has a chance to freeze and expand.
Use Clean Rock for Backfill
Instead of backfilling with dirt, the space immediately behind the retaining wall must be filled with clean, crushed drainage rock. This allows water to quickly drop down to the drain pipe rather than pooling and freezing behind the blocks.
Reinforce with Geogrid
For walls taller than a few feet, or walls supporting extra weight, geogrid reinforcement is absolutely essential. This heavy-duty mesh grid is sandwiched between the courses of block and extends several feet back into the compacted soil, essentially locking the wall and the hillside together into one unified, unmoving structure.
Leave it to the Minnesota Hardscaping Pros
Building a retaining wall that can survive decades of Minnesota winters is back-breaking work that requires precise engineering, heavy equipment, and a deep understanding of our local soil and weather dynamics.
Whether you're dealing with a collapsed wall that needs replacing, or you're looking to upgrade your Twin Cities property with a new hardscape feature, Monson Lawn and Landscaping is here to help. We understand the unique challenges of Minnesota hardscaping and build walls designed to stand the test of time.
Ready to get started? Contact us today for a quote on your next landscape project!