Retain This! …A primer to retaining walls.

“Hey, I just want to flatten out my backyard so the kids can play” was my customer’s reason for initiating a recent project. One way to achieve that level yard is to re-grade (move the soil around )  the yard and add a low wall that retains the earth to create that more usable level property.  1

There are a lot of issues one intuitively knows about retaining walls we learned at the beach as little kids. I.e. when you have a deep hole-don’t step too close to the edge of the hole, or the sand will collapse.  The steeper the slope of the sand next to the hole the more likely the bottom of the hole will settle.   The deeper the hole, the more careful you have to be when digging.  Water near the hole quickly affects the stability of the hole…Etc.

Each of the 5 types shown here have different characteristics in terms of appearance, cost,  longevity and viability to the environment.

Segmental block: medium cost, lego-like construction, reinforced with layers of horizontal mesh that bond with the uphill soil.

Concrete: medium to high cost, monolithic construction, strongest resistance to movement

Sheet piling: medium to high cost, difficult to install, also appropriate for marine bulkheads, requires maintenance,

Stone retaining wall: highest cost, requires skill labor to install, nicest appearance, can be reinforced or dry laid

Railroad tie: lowest cost, easiest to build, shortest life-span

Accordingly, there is more that goes into the retaining wall , than meets the eye. Soil characteristics like how much clay or slippery silt the wall rest on can be critical. The amount of water in the soil and the direction it flows  can also create havoc for walls- and has to be addressed in the design.

Much of the stability of the retaining wall comes from the footing and the way that the wall itself is reinforced. So – think carefully of a bookend and how it keeps the books from  falling over. It’s really the weight of the books resting on the flange of the bookend that stops the rotation of the books from falling over.  Similarly many footings of the retaining wall has a “heel that is much longer than the “toe” to help use the soil weight to help keep the vertical wall stiff and resistant to toppling over.

Likewise think of a diving board – the longer it is,  the more bouncy it is towards the end. In effect the retaining wall behaves like that diving board too. So the taller the wall- the more heavily reinforced it will need to be and the larger the footing that will be required…See the illustration below:retaining-wall-drawing

When the soil or water starts to win the battle , the wall starts to lean- wrong way- like below…and it’s game over. You don’t want the wall on your car or your passenger!


We can help you out with your situation call us now 914 980 5532, ask for Steve!