Interpretation of pressuremeter unloading tests in sands

The paper presents a new unloading analysis for pressuremeter tests in sands. The analysis is based on a strain-hardening (or softening) plasticity model in which the angles of friction and dilation are assumed to be a function of the state parameter. A series of numerical analyses using the state parameter-based constitutive soil model suggest that there is a linear correlation between the slope of the pressuremeter unloading curve, when plotted on logarithmic scales, and the initial state parameter. As a result, the initial state parameter, and therefore the friction angle of the soil, can be deduced from the measured slope of the pressuremeter unloading curve. The validity of this new unloading analysis has been confirmed with the results of a number of field and laboratory pressuremeter tests.