How to Tell What Kind of Retaining Structure You Have

Segmental units, concrete, stone and filled cages appear across more than one mechanism. A face light enough to handle by hand can front a reinforced block that holds ground a masonry wall of the same appearance could not, because in that case the visible wall is a facing and the reinforced fill behind it is doing the work.

On a nailed slope the same reversal applies with a different vocabulary. Mesh, a sprayed shell, discrete panels and a vegetated wrap are all facings holding only the material between the reinforcement heads, which is why the same retention appears as a hard grey face in one place and a green one in another with nothing structural having changed.

Some clues are real, though none of them is conclusive on its own. A stem that is slender for the height it holds suggests bending rather than mass, because a cantilever stem is thin precisely because it works in bending. A very wide base, or a face with the bulk of a mass section, points the other way.

Dry-laid, cage-built and stacked forms take up distortion by deforming, while rigidly jointed mass concrete and mortared masonry record the same movement as cracking. How a structure has responded to movement therefore says something about how it is jointed, even when it says nothing about what is behind it.

Records outrank observation here, because the position, depth and extent of buried elements cannot be verified later by inspection. Construction records, drainage drawings, a structural design, an approval file or a previous owner's handover pack will settle in minutes what a week of looking will not.

Where records are partial, the questions worth putting to them are narrow: how far back does any reinforced zone extend, where does the drainage collector discharge, and was the wall formed before or after the ground in front of it was removed. That last question alone separates an embedded wall from everything else.

Outlets are informative because every mechanism relies on drainage and each arranges it differently. Weeps through a face, a collector discharging beside the wall, or drainage taken out through a treated slope face each belong to a different arrangement, and their absence is itself a finding worth recording.

Coping and cap lines are the other readable termination. A coping projecting past both faces with a drip belongs to a wall designed to shed water clear of its own mass; a flush capping is doing very little of that, whatever the wall behind it turns out to be.

A mass wall stops at the back of its own section, with undisturbed or ordinary backfill beginning there. A reinforced soil structure continues back into the slope well beyond its face. That difference is not visible, but it is sometimes inferable from what has happened behind the face over the years.

Settlement of the surface some distance back, voids opening behind facing units, or a strip of ground behind the wall that behaves differently from the rest of the garden are all worth photographing and reporting rather than making good. So is any history of trenching, planting pits or posts behind the face.

A wall leaning gradually tells a different story from one cracked along a line, and a face bulging locally tells a third. In a reinforced soil structure a bulging face usually reports the relationship between facing and reinforcement, or compaction close to the face, rather than weakness in the units themselves.

The useful contribution an owner makes is a record rather than a conclusion: where, how much, since when, and whether it changes with the seasons or after heavy rain. Distinguishing the mechanisms behind those patterns is what a professional assesses.

Unknown is a legitimate and useful finding. An existing wall of unknown construction should not be assumed to have a foundation, a damp-proof course or any reinforcement, and the same caution extends to assuming which mechanism it uses.

What follows from unknown is practical rather than dramatic: nothing is dug behind, in front of or at the toe without advice; drainage outlets are found and kept clear; observations are recorded over time; and any proposal to change levels near the structure starts with a professional rather than with a quotation.