Most retaining walls in Michigan fail because of water. When rain and snowmelt saturate the soil behind a wall, that soil gets heavier and presses harder against the blocks. In winter, the same water freezes and expands, and each season pushes the wall a little further out of line. A wall set on a compacted base, backed with clean drainage stone, and fitted with drain tile at its footing lets water escape before pressure has a chance to mount.
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A failing retaining wall looks like a stone problem, so it’s natural to blame the block. Look closer, though, and the cause almost always sits behind the wall or under it, in soil and water nobody sees once the job is finished.
What a Retaining Wall Holds Back
A retaining wall keeps a slope from sliding into your yard. After a week of spring rain, every gap between the soil grains fills with water, and the slope gets heavier. Trapped water also presses outward on its own, the way water in a bucket presses on the sides. Engineers call this hydrostatic pressure, and it grows with depth, so the bottom of a wall takes the hardest push.
The Kalamazoo area sees about 35 inches of precipitation a year and sits in the Lake Michigan snow belt, so a whole winter of snow tends to melt into the ground over a few weeks each spring. The ground here also freezes deep. Michigan’s building code sets frost protection for foundations at 42 inches below grade. Water in the soil behind a wall expands when it freezes, and every freeze-thaw cycle between November and April is another chance to move the blocks.
Why Retaining Walls Fail in Michigan
When we’re called out to a failed wall, the cause is usually one of a few problems you can’t see from the patio.
Water Has Nowhere to Go
The most common problem is native soil packed straight against the back of the wall. Soil holds water like a sponge. With no drainage stone or drain tile to carry that water away, it sits against the blocks after every storm and adds pressure the wall was never designed to hold. Over a few seasons, the middle of the wall bows forward or the top starts to lean.
Frost Heave Pushes the Blocks
Wet soil behind a wall turns into a slow-moving jack in winter. As ice forms, the soil swells and pushes on the back of the blocks. When it thaws, the blocks don’t slide back into place. After enough winters, courses that started level have stepped out of line and joints have opened up.
The Base Settles
A segmental block wall sits on a trench of compacted crushed stone, with the first course partly buried below grade. When a crew skips the compaction, digs too shallow, or sets the first course on topsoil, the wall settles unevenly. One low corner is enough to tilt every course stacked above it.
Taller Walls Skip the Geogrid
Past a few feet of height, most block walls need layers of geogrid reinforcement, a strong mesh laid between courses and extended back into the slope. The geogrid ties the wall and the soil behind it into one heavy mass. Leave it out, and the wall has only its own weight to resist a slope that can outweigh it once it’s wet.
Surface Water Pours In From Above
Sometimes the water comes from the house. Downspouts that empty near the top of a wall, or a yard graded toward it, send roof and lawn runoff straight into the soil the wall is holding back.
The Material Can’t Handle the Load
Landscape timbers are cheap and quick to install, and they rot once they stay wet. A timber wall holding back a hillside will give out long before a block or natural stone wall would.
Michigan Soil Changes the Drainage Plan
Southwest Michigan doesn’t have one soil type. Much of the Kalamazoo area sits on glacial outwash, the sand and gravel left behind by meltwater, which drains quickly. The morainal highlands hold denser glacial till with more clay in it, and low spots can hold poorly drained muck.
Clay-heavy soil holds water against a wall for days after a storm and heaves hard when it freezes. Sandy soil drains well, but it can wash out through the joints between blocks, leaving hollow pockets behind the face. Plenty of yards have both on the same slope. Checking what’s under the grass during design tells you how much drainage the wall will need.
Warning Signs Your Retaining Wall Is Failing
Retaining walls rarely come down overnight. They show warning signs first, usually over a few seasons:
- Leaning or bulging. The top tips toward the yard, or the face pushes outward in the middle.
- Shifted or cracked blocks. Courses have stepped out of line, or individual blocks have split.
- Water at the face or base. Water weeps through the joints or pools at the bottom after rain.
- Soil washing out. Sand or dirt trickles out between blocks, especially after storms.
- New gaps nearby. A space has opened between the wall and a patio, walkway, or set of steps.
The earlier you catch these signs, the more of the wall you can usually save.
Can a Failing Retaining Wall Be Repaired?
Sometimes. If the base is sound and the problem is water trapped behind the wall, a crew can often take the wall down to the affected courses, add drainage behind it, and reset the original block.
If the base has settled or the lower courses have shifted, a partial repair won’t hold. New courses stacked on a failed bottom half will follow it forward, so the fix is a new wall on a new base, with drainage designed in from the start.
How Drainage Prevents Retaining Wall Failure
A well-drained wall gives water a path out of the soil before pressure can mount. The path has five parts:
- Clean drainage stone behind the wall. About a foot of crushed, washed stone fills the space directly behind the blocks. Water drops through it instead of sitting against the wall, and the stone gives frozen ground room to move without shoving the face.
- Perforated drain tile at the base. A pipe along the bottom of the drainage stone collects the water and carries it out to daylight or a drain.Filter fabric between stone and soil. Fabric keeps fine soil from migrating into the drainage stone and clogging it, so the system keeps working for decades.
- A compacted base below grade. The first course sits partly buried on compacted crushed stone, which holds the wall level and lets water move out from underneath.
- Grading that sends water elsewhere. A shallow swale above the wall and downspouts routed away from it keep roof and yard water from soaking the slope in the first place.
None of these parts show once the wall is finished, which makes them the easiest place for a low bid to save money. Leave them out, and a wall that should look the same after twenty winters can need replacing after five. We covered more of that math in Doing It Right the First Time.
Drainage belongs in the plan for any hardscape on a slope, since a patio above a wall or steps cut through it add their own runoff.
What to Ask Before You Hire a Retaining Wall Contractor
Every contractor will show you the block. Ask about the parts you won’t see:
- What goes behind the wall? A good contractor will describe the drainage stone, drain tile, and fabric, and tell you where the water exits, before you have to press.
- How deep is the base, and how is it compacted? Listen for crushed stone, compaction in lifts, and a buried first course.
- Does my wall need geogrid? Ask how they decide and how far back into the slope it will extend.
- Where will my downspouts and yard water go? The answer should cover the whole slope, not only the wall.
- Can I see walls you installed a few years ago? Any wall looks good on install day. Photos and references from older projects show how a contractor’s work holds up through Michigan winters.
Retaining Walls Designed for Michigan Winters
At Serenity Outdoors, Jon designs every retaining wall personally, starting with how water moves across your yard. Our team is ICPI certified through CMHA and trained in professional drainage installation, so the drainage plan is part of the design from the first sketch. Isaac and Daniel install each wall to match it.
If a wall on your property has started to lean, or you’re planning one for a slope, bring us your questions. We’ll walk the site with you and give you a straight answer about what it needs.