Site investigation · Laboratory: strength & consolidation

Collapse potential (oedometer) calculator

Collapse potential from the strain on wetting at constant stress, with the usual severity classes.

Standard: ASTM D5333 · Jennings & Knight

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Input	Value	Unit
Initial height	20	mm
Height before wetting (at stress)	19.12	mm
Height after wetting	18.05	mm
Initial void ratio	0.86

Diagram for the worked example

Collapse potential ΔH/H0 = 100*(19.12-18.05)/20 = 5.35 %
Change in void ratio = 5.35/100*(1+0.86) = 0.09951
Severity = IF(5.35<0.1,"none",IF(5.35<=2,"slight",IF(5.35<=6,"moderate",IF(5.35<=10,"moderately severe","severe")))) = moderate

Oedometer consolidation test — Lab sheet: e–log σ' curve, Cc, Cr, Casagrande preconsolidation pressure, mv per stage and cv by Taylor's…
Triaxial test (UU / CU / CD) — Mohr circles and failure envelope from triaxial specimens: su for UU, c′ and φ′ for CU (with pore pressure)…
Unconfined compression test — Stress–strain with area correction, peak qu, su = qu/2 and E50 secant modulus.
Direct shear test — Peak (and residual) failure envelopes from shear box results.
Permeability (constant / falling head) — Hydraulic conductivity from constant- or falling-head tests, corrected to 20 °C.
Stress paths (MIT p′–q) and strength fit — Total and effective stress paths from triaxial data, with the Kf line fitted to give c′ and φ′.
Coefficient of consolidation (root-time & log-time) — cv from Taylor's t90 and Casagrande's t50, with permeability from k = cv·mv·γw.
Free swell & swell pressure (oedometer) — Free swell strain under seating load and swell pressure from the constant-volume or load-back method.
Residual strength: ring shear — Residual friction angle from a regression through the origin and a free-intercept fit.
Vane shear (lab / field) — Undrained strength from peak and remoulded torque, sensitivity and Bjerrum's plasticity correction.

For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.