The combined effects of loading frequency and other parameters on dynamic properties of reconstituted cohesive soils

An advanced triaxial testing system has been developed to perform dynamic tests on soils over a wide range of shear strains and loading frequencies. Internal measurements of load and displacement eliminate many sources of potential measurement error. Local measurement of the shear wave velocity, which may then be converted into the maximum shear modulus (G_max), is accomplished in the same apparatus using bender elements on the same specimen. The effect of loading frequency on four reconstituted cohesive soils has been investigated, and values of obtained through bender element testing are compared with those obtained through triaxial testing. Higher loading frequencies are observed to both increase shear modulus and decrease damping ratio. Values of G_max obtained through bender element testing are not consistent with results from triaxial testing, differing by as much as 30% depending on the soil type, consolidation stress history, and anisotropy. Normalizing shear modulus reduction curves obtained at a given loading frequency by values of G_max obtained through the same testing procedures results in normalized shear modulus reduction relationships which are independent of frequency for a given soil. Two soils with similar plasticity indices but very different mineralogies were observed to be affected similarly by changes in loading frequencies, but the normalized shear modulus reduction and damping ratio curves of the mixed soil more closely follow those of the primary constituent of the mixed soil.