Rebuild the gap with loose stones. Every stone must sit on the one below with its centre of mass over solid support; the whole wall must carry a push on its crest.
Solid line: load that tips or slides the stones above each course (per metre of wall). Dashed: the load you need to withstand (load × 1.5 safety factor).
The science
What you see. A double-faced dry stone wall: no mortar, only gravity, friction and the way stones overlap. Stones are modelled as boxes (drawn as rounded stones), density 2600 kg/m³ × 0.85 shape factor.
Rule 1: support. A stone rests on the highest tops beneath it (within 30 mm; smaller “pinning” stones shim the rest). It stands only if its centre of mass lies inside the convex hull of those contact areas: ΣF = 0, ΣM = 0.
Rule 2: crest load. For each course interface (a “cut”) and each 1 m window of wall, the block above the cut has weight Wu and its centre of mass sits e from the nearer edge of the contact strip. A push q (N/m) at the crest tips it when q·L·(ztop−zcut) > Wu·e and slides it when q·L > μ·Wu (friction μN ≥ |Ft|).
Rule 3: interlock. Running bond (vertical joints that do not line up with the joints below) and through-stones (as wide as the wall) bind the faces. Model value, not from literature: interlock factor f = 0.6·bond + 0.4·ties raises sliding resistance by ×(1 + 0.5f) and tipping resistance by ×(1 + 0.3f).
Score. Stability = min( qcrit / (1.5 q), 0.7·mean(local) + 0.3·min(local) ). Worked example: a single 1.0 × 0.6 × 0.4 m block weighs W = 2600·0.85·0.24·9.81 = 5 203 N. With μ = 0.6 it slides at 0.6 W = 3 122 N/m and tips at W·0.3/0.4 = 3 902 N/m, so the limit is 3 122 N/m (sliding).
Assumptions and gaps. Rigid boxes, 2D cross-section per metre, static load, no earth pressure, no frost or root action, no real batter or hearting model, friction values are typical round numbers (model values) and the scene is a stylised Yorkshire-like valley, not a survey of a real place. Real walling relies on training and local stone: this is a virtual exercise only; real stones are heavy and sharp, so do not copy it from a screen.
Sources. Statics textbooks for rigid-body overturning and Coulomb friction; dry-stone walling guidance on running bond and through-stones [to verify against a named craft guide]. No data is quoted from a specific study.
Made with Blender models and Three.js.