Converting between power law and hyperbolic representations of stiffness decay with strain

ABSTRACT: Repeatable data for shear modulus is readily obtained from small cycles undertaken as part of a cavity expansion test. In all soils these data follow a hysteretic path that a high resolution pressuremeter can capture and use to describe the stiffness degradation with strain characteristics. This response is normally modelled as a power law. The standard cycle is not expected to see shear strains below 0.01% and hence does not measure the elastic shear modulus, Gmax, found at shear strains nearer 0.001%. By contrast, laboratory testing of small strain stiffness is normally represented by a hyperbolic function where Gmax defines the starting plateau, and in this form is readily incorporated into design software. It is always important that laboratory and insitu data are compared and if possible aligned. This paper considers potential methods for translating power law data into hyperbolic relationships.