Centennial Retaining Walls

Late July, around six in the evening. A cell that looked harmless over the foothills an hour ago is putting most of an inch on your yard in forty minutes, and all of it has to go somewhere. Grass can't take water in that fast, so it sheets. It finds the low line, gathers, and pours over whatever stands in its path. Often that's a retaining wall nobody asked about surface runoff.

Next morning everything looks fine, which is the trap. A few days later one panel holds a dark stain while the rest dries, a divot opens in the lawn above, and the wall is carrying a load nobody drew. Storms like that are what we design for out here.

Groundwater and runoff are two different problems

Almost every wall gets built with the first in mind. Moisture works through soil, reaches the back of the concrete, and needs a path down and out. Rock, fabric, perforated pipe, an outlet. Standard, and we do it every time.

Surface runoff is a different animal, and it's the one that hurts walls in Centennial. It doesn't seep. It arrives in minutes with enough energy to move soil, and it goes wherever the grade sends it. On the terraced back yards through Piney Creek and Walnut Hills, that grade got set decades ago by somebody thinking about how the lawn looked, not about a cloudburst. So we walk uphill before we design anything. Where the water starts matters more than what the wall is made of.

Where a forty minute storm sends its water

What that hour does to a wall somebody built cheap

Here's the wall we get called about. Native clay packed straight against the concrete, no rock, maybe a few weep holes drilled through the face as an afterthought. In ordinary weather it behaves, because water moves through that soil slowly. Then a storm dumps in forty minutes, the fill takes on all it can hold, and pressure at the base of the wall climbs hard overnight.

Do that enough times and the wall tells you. The top tips out a little further each season. A horizontal crack opens across the stem. Cap joints spread. Weeps plug with fines because nobody put fabric behind them. Our position, plainly: a modest wall with real drainage outlasts a heavy wall with none. Every time. If the budget forces a choice between thickness and drainage, buy drainage.

The walk we take the day after a heavy storm

• One panel still dark while the rest of the wall has dried
• Water standing anywhere on the terrace above instead of running off it
• Fans of silt below the weeps, meaning fines are moving out of the backfill
• A settled trough in the lawn above, tracking the line of the old trench
• Cap joints that have opened since the last time you looked
• Mud or gravel washed onto the walk or patio below the wall
• The drain outlet, checked to confirm water is actually leaving through it

The season to build, and the season that tests it

We build walls year round and the concrete is the easy part in any month. Footings go in below frost, and cold weather placement is routine with warm water, accelerators, and blankets. Backfill is where winter interferes, because frozen chunks of soil leave voids that show up as settlement the next spring.

Late summer through fall is the window we push people toward. The ground is dry enough to excavate cleanly, the backfill compacts honestly, and there's time to shape the grade above before snow. Then winter runs its own inspection: saturated backfill freezes, expands, and pushes, and a wall without drainage takes that abuse from November through March. By April you'll know what you bought.