Behavior of Rigid Footings on Gravel under Axial Load and Moment

A laboratory testing program was conducted to study the settlement and rotation response of rigid square footings under combined axial load and moment. A total of 17 tests were performed in which the size of the footing, footing embedment, axial load, and load eccentricity were changed. The test soil consisted of a fine and well-graded gravel contained in a box with dimensions: $1.52\times 1.52\mathrm{m}$ $(5\times 5\mathrm{ft})$ cross section and $0.91\mathrm{m}$ $\left(3\mathrm{ft}\right)$ deep. The soil was compacted in layers $150\mathrm{mm}$ $\left(6\mathrm{in.}\right)$ thick to an approximate relative density of 84%. In each test, the axial load, moment, settlement at the center of the footing, and footing rotation were measured. Concentrically loaded footings with different sizes exhibited a similar behavior in terms of the applied stress-normalized settlement (settlement divided by size of footing) response. The analytical model proposed was based on such normalized response as an input, and it was calibrated to account for the change in soil stiffness with confinement. The formulation captures the inherent nonlinear deformations of the soil with load and the coupled nature of settlements and rotations of footings under axial load and moment. The model was tested by comparing calculated values with laboratory measurements from tests not included in its calibration. The comparisons showed a satisfactory agreement between calculations and measurements, bringing confidence in the analytical formulation proposed and the methodology used.