A customer sent these photos in of a dry bluestone retaining wall that failed on Queen Anne's Rd in Harwich, MA. Although the landscape masons laid the stones properly for the most part, they used small stones that don't have a lot of weight to them and don't reach deep into the wall, they didn't lay the foundation below grade, and they didn't use a compacted crushed stone backing. A few Small stones can be used effectively in the face of a dry stone wall, but only when sufficient weight from above locks them in. In order to last, all dsy stone walls must contain stones that reach deep into the wall, must include a foundation below grade, and a deep layer of compacted stone of various sizes. The above photo shows a common type of landscape stone construction on Cape Cod. Unfortunately, the stone is inadequate for the purpose.
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