Determination of the dynamic shear modulus and the depth of the dominant layer of a vibrating elastic medium

Abstract

It is shown that errors up to 20 per cent can arise in the estimation of the dynamic shear modulus of the foundation under a vibrating structure if the foundation, as hitherto generally assumed, is regarded as an isotropic half-space instead of an isotropic stratum on a relatively rigid bed which, in many practical cases, is a more realistic model. The problem then reduces to the determination of the depth and the shear modulus of some layer immediately under the structure, for this governs more the response of the structure than does the average modulus of the entire medium.The present work, based on recent results of the torsional vibration of a rigid circular body on an elastic stratum, corrects these errors by first establishing in a novel manner the depth of this dominant layer and then determining its shear modulus. Test procedure and the choice, with magnitude, of parameters to be used in order to obtain reliable results are given. The work also gives the method of detecting cases in which the vibrating medium cannot be replaced by the theoretical model on which it is based.