Why retaining walls fail in New England, and it is not the block

If you have a retaining wall that has started to lean out, bulge in the middle, or open up at the joints, the block is almost never the problem. Modern segmental wall block is good product. What failed is underneath it and behind it, and in New England there is usually one culprit.

Water is the whole story

A retaining wall is holding back soil, and saturated soil is dramatically heavier than dry soil. Worse, water that cannot drain out from behind a wall freezes. Frozen water expands, and it expands in the only direction available, which is outward through the face of your wall.

That is why walls here fail in a way they do not in milder climates. It is not one catastrophic event, it is a few dozen freeze and thaw cycles quietly pushing the wall out a fraction at a time until you can see it from the driveway.

What should be behind a wall you cannot see

• A compacted base below frost-affected ground, deeper than most people expect
• Drainage stone behind the full height of the wall, not a token strip at the bottom
• Filter fabric separating that stone from the soil, so it does not silt up and stop draining within a few years
• A perforated drain pipe at the base with somewhere to actually go
• Backfill compacted in lifts as the wall goes up, not dumped in at the end

None of that is visible when the job is done. All of it is what decides whether the wall is still straight in ten years. It is also, conveniently, the easiest place to save money on a quote, which is why cheap walls are cheap.

How to read a quote

You do not need to know construction to ask two questions. Ask how deep the base is going and ask what is going behind the wall. A contractor who builds properly will answer immediately and in detail, because it is the part they are proud of. A vague answer about it being "done to spec" is an answer.

When a wall needs an engineer

Above roughly four feet, or where a wall is holding up a driveway, a structure, or a slope with a surcharge on top of it, you are past landscaper territory and into engineered design. Anyone who tells you otherwise is either inexperienced or hoping you do not ask. We will say so when a job is beyond us, because a wall that fails is a much bigger problem than a wall that cost more.

On wooded, sloped ground, which describes a lot of properties in Sharon and the western half of the South Shore, drainage matters even more, because water comes off that ground fast and arrives at your wall in volume.