Modulus of subgrade reaction

Modulus of Subgrade Reaction k_s — Interactive Calculator

Based on ranges after Das (1999). Enter load (q) or desired settlement (s) to compute the other values and visualise springs.

Soil family Sand (dry / moist) Sand (saturated) Clay Condition / Density Foundation plan (for visual) — Width (B) in m Foundation plan — Length (L) in m Applied pressure / contact stress q (kN/m²) Or desired settlement s (mm) — optional (if entered, q will be computed)

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Units: input q in kN/m², widths in m. Table stored k_s ranges are in MN/m³ — converted to kN/m³ internally (1 MN/m³ = 1000 kN/m³).

Results

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Numeric outputs

Interpretation & Guidance

Visualisation

Springs show relative stiffness; settlement scale is exaggerated for clarity.

Table used (Das, 1999)

Sand (dry/moist) — Loose: 8–25  MN/m³

Sand (dry/moist) — Medium: 25–125 MN/m³ Sand (dry/moist) — Dense: 125–375 MN/m³ Sand (saturated) — Loose: 10–15 MN/m³ Sand (saturated) — Medium: 35–40 MN/m³ Sand (saturated) — Dense: 130–150 MN/m³ Clay — Stiff: 12–25 MN/m³ Clay — Very stiff: 25–30 MN/m³ Clay — Hard: >50 MN/m³

These are indicative ranges — for design, prefer in-situ plate load tests or cone penetration estimates where possible.