The Dry-Stone Retaining Wall Bound: Batter, Base Thickness, and the Height a Vertical Face Cannot Reach

Dry-stone retaining walls are traditionally built with a batter — the face leaning back into the hill — and traditionally defended by assertion. This paper computes what the batter is worth. Active earth pressure is evaluated by the Rankine formula for a stated retained soil of unit weight 18.0 kN/m³ and friction angle 30 degrees, and overturning, sliding, and the position of the resultant are checked, with factors of 1.5 required and the resultant held within the middle third of the base, for vertical-faced and battered dry-stone walls retaining 1.0 m to 4.0 m. The rule originated here: a vertical wall needs a base thickness of 0.58 times the retained height (1.735 m at 3.0 m); a wall battered at 1 in 6 needs a base of 0.538 times the height (1.615 m at 3.0 m) and, more importantly, about a fifth less stone — 4.095 m² of cross-section against 5.205 m² at 3.0 m. Under a stated practical base cap of 1.50 m, a vertical face reaches a retained height of 2.55 m and a 1-in-6 battered face reaches 2.75 m; 2.75 m is therefore a height a vertical face cannot reach within the cap. The paper also disproves, with arithmetic, the belief that a vertical dry-stone wall retains as much soil as a battered one built from the same volume of stone: at 3.0 m retained height and identical cross-sectional area of 5.205 m², the battered wall's overturning factor is 3.857 against the vertical wall's 3.010, a gain of 28.1%, while a vertical wall given only the battered wall's smaller volume fails the middle-third condition outright. This study is simulated, not measured, and no wall described here has been load-tested; every result is conditional on the wall being drained, as stated in the methods.