Prediction of Modulus of Elasticity and Its Impact on Settlement-Paper

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The study evaluates how estimates of soil modulus of elasticity (E) affect predicted foundation settlement. Two 2 × 2 m footing load tests were conducted at 7.5 m depth on silty sand, with applied pressure up to approximately 354 kPa. Measured settlements were 4.70 mm and 4.14 mm. Elastic-theory back-calculations from the tests gave E values of about 91 MPa and 103 MPa.<br /><br />These field-derived values were compared with 19 empirical correlations based on Standard Penetration Test (SPT) N-values, as well as settlement predictions from SETTLE-3D and PLAXIS-3D. SPT correlations produced E estimates ranging from 11 to 125 MPa. The ratio of field-derived to correlation-based E ranged from 0.8 to 9.3, typically around 3–4. Several correlations, including those by Chaplin, D’Appolonia, Al-Sheyea and Clayton, aligned more closely with the field results.<br /><br />Both software programs predicted settlements that increased with applied pressure. SETTLE-3D estimates were modestly higher than measured settlements—about 2–6% at lower pressures and roughly 30% at the maximum pressure. PLAXIS-3D predictions were substantially higher: about 30% above measured values at low pressures and more than double at the maximum pressure. Differences between the two programs ranged from 15% to 85%.<br /><br />The findings emphasize that modulus selection strongly influences settlement predictions. Field load tests can provide useful calibration, while empirical SPT-based correlations and numerical models may yield substantially different results.

Keywords

soil modulus of elasticity

foundation settlement

footing load tests

silty sand

elastic theory

Standard Penetration Test

SPT correlations

SETTLE-3D

PLAXIS-3D

settlement prediction