Modulus of subgrade reaction

Scope

The calculation relies on the highly simplified model of assuming that, under a shallow foundation, the relation linking at every point the vertical displacement y of the footing and the pressure p exerted by the soil in reaction to this displacement has the form:

Such a model is useful for evaluating the distribution of forces under a foundation. The rules applied by CiviLab give an evaluation of the coefficient k from pressuremeter tests, in accordance with Annex F of NF P 94-261 (Eurocode 7) and Fascicule 62 Title V.

Principle

The principle is to evaluate the settlement s of the foundation under a uniform pressure q. The value k_v of k for long-term loads is then derived by:

Settlement is calculated using the Menard pressuremeter method, from the moduli E_M measured on the profile and divided into slices of thickness B/2 under the footing.

Cases covered

• Homogeneous soil: a single pressuremeter modulus under the footing;
• Heterogeneous soil: moduli E₁ to E₁₆ per slice, with calculation of the equivalent modulus E_c;
• Isolated footing, strip footing and raft of limited width;
• Long-term loads (k_v) and short-term loads;
• Foundation geometry taken into account: width B, length L, embedment D;
• Calculation according to Eurocode 7 (NF P 94-261) or Fascicule 62 Title V.

CiviLab allows you to:

• Use the pressuremeter profile entered in the software directly, without re-entering the moduli;
• Calculate the settlement s then the modulus of subgrade reaction k_v of the foundation;
• Obtain the equivalent modulus E_c in heterogeneous soil;
• Compare several foundation geometries on the same borehole;
• Save and print the results properly;
• Organize calculation notes by project and by borehole.