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Spread Footing Settlement on Cohesionless Soil — Hough Method, AASHTO LRFD §10.6.2.4.2 (U.S. units)

Layer-by-layer settlement with the 2:1 stress distribution, and the permissible net contact stress that produces a target settlement — the service-limit check that usually governs footings on soil.

Footing and load

B ft

L ft

Service load P (net) kip

Permissible settlement in.

Soil above footing base ft

Its unit weight pcf

Layers below the base — one per line: thickness (ft), effective unit weight γ′ (pcf), C′ from AASHTO Fig. 10.6.2.4.2-1

Results

Total settlement vs permissible—

Applied net stress P/(BL)—

Permissible net contact stress q_pn (load)—

Layer	z_mid (ft)	σ′_o (ksf)	Area (ft²)	Δσ′_v (ksf)	ΔH (in.)	Σ (in.)

AASHTO LRFD§10.6.2.4.2 (Hough method, Eq. 10.6.2.4.2-3; Fig. 10.6.2.4.2-1 bearing capacity index C′; C10.6.2.4.2 layer thickness ≤ 10 ft; 2:1 distribution). Clause numbers only.

VerifiedCaltrans Geotechnical Manual, Shallow Foundations for Bridges (2021), Appendices 1 and 2: every tabulated value reproduced to the source rounding; permissible net contact stress 6.3 and 5.6 ksf. The two appendices read different C′ for the same N1₆₀ (32: 110 vs 102) — C′ is a user input.

Preliminary calculation tool. Final design requires the full text of the referenced standard (see the sources on this page) and review by a licensed PE.