Segmental wall

A conventional (gravity) segmental retaining wall of dry-stacked concrete units, per foot of wall, by the NCMA approach to external stability: the units with their infill as a battered gravity wall, plus the interface shear between units from the manufacturer's tests.

Inputs of the segmental wall #

• Units: number of courses, unit height and depth, setback per course (the batter ω = atan(setback / unit height)), the in-place unit weight with the infill, the embedment (soil in front of the base) and the leveling pad thickness (drawn).
• Retained soil: φ, the wall friction δ on the back of the units (NCMA uses 2/3 φ for a conventional wall), the backfill slope, γ and a uniform surcharge (dead or live: a live surcharge drives the wall but does not resist).
• Stability: the allowable bearing pressure, the base friction coefficient μ, the interface shear intercept and angle a_u and λ_u from the manufacturer's ASTM D6916 tests, the passive resistance factor (NCMA neglects it: 0), the factors of safety (NCMA minimums prefilled: sliding 1.5, overturning 2.0, interface shear 1.5) and the eccentricity limit.

Auto-design (editor toolbar) varies the unit depth (12 to 30 in.); the number of courses, unit height, setback, soil, interface values and loads are kept. Objective: least unit volume. Every other input is kept; see Auto-design.

Checks performed #

The drawings show the wall section (the units with their setbacks, the leveling pad, the backfill, the soil in front, the surcharge, the horizontal earth pressure on the back plane, the main dimensions) and the service bearing pressure. The leveling pad design, drainage aggregate, drain pipe, cap units and adhesive are not part of the calculation.

Limitations #

• Conventional (unreinforced) walls only. Geogrid-reinforced walls (internal stability, pullout, connection strength, the reinforced mass) are not offered: the NCMA Design Manual for Segmental Retaining Walls is not on file and no free worked example allowed a verified implementation.
• The NCMA bearing capacity (Meyerhof with B' = B − 2e) is not computed: enter the allowable bearing pressure.
• Water, seismic loads and global stability are not included; the passive resistance of the embedment is neglected by default.

Verification examples #

Verification status: 7 values compared in 1 example (0 published, 1 hand calculations from the cited equations): 7 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: written without the code document on hand, and confirmed only in part through published examples.

The NCMA design manual and its worked examples are not on file (research/DOCUMENTS_NEEDED.md). Hand calculation in closed form (backend/tests/test_verify_segmental_wall.py): three 8 × 18 in. courses with a 1 in. setback, φ = 32°, δ = 21.3°, a_u = 1000 lb/ft, λ_u = 30°.