Static and dynamic rocking stiffness of shallow footings on sand: centrifuge modelling

Abstract

Small-strain foundation response has mostly been studied analytically, with limited experimental verification against 1g physical model tests. This paper revisits the problem of small-strain foundation response, conducting a series of centrifuge model tests, aiming to eliminate the limitations of 1g testing. A centrifuge modelling technique is developed, combining static pushover and dynamic impulse testing for similar systems. To allow for derivation of meaningful insights, a novel procedure for in-flight measurement of the distribution of shear modulus with depth is also developed. The latter combines spectral analysis of surface waves (SASW) measurement of the shear modulus G 0 at the surface, and estimation of the distribution of the shear modulus G with depth using acceleration measurements in shaking tests. A novel centrifuge tube–actuator is developed and employed to discharge spherical projectiles against single-degree-of-freedom models lying on shallow foundations on sand. This allows generating dynamic impulse excitation, which is used to measure the small-strain dynamic rocking stiffness. The developed actuator is versatile, and was also used for in-flight SASW testing. The centrifuge model tests are shown to confirm the widely used and well-known formulas. This good agreement can also be seen as a confirmation of the validity of the developed experimental techniques.