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Abstract
The mechanics of fiber reinforced sand has been comprehensively studied in the past few decades, especially by means of large deformation monotonic behavior and static liquefaction. However, little attention has been paid on shear modulus (G) and damping ratio of fiber reinforced soils within a range of strains from about 10-4% to 10-1% (so called small-to-medium strain range) under dynamic loading. The motivation behind this work is to fill this literature gap and provide a comprehensive database of dynamic experimental data covering a wide range of sand types and fiber contents in a range of strains which is of major interest in daily engineering practice and also in soil dynamics research.
A series of bender element and resonant column tests are conducted to investigate the properties of polypropylene fiber-sand mixtures, and the major contributions of this thesis can be concluded as:
i. Under isotropic stress path, the inclusion of fiber tends to decrease the small strain shear moduli Gmax(vh) and Gmax(hv).
ii. Fiber content and fiber size are critical factors that dominate stiffness anisotropy of sand-fiber mixtures; the growth of fiber content and fiber length results in a decrease of stiffness anisotropy expressed as [Gmax(hv)/F(e)]/ [Gmax(hh)/F(e)].
iii. An expression for Gmax of sand-fiber mixtures subjected to isotropic stress path is proposed and verified, which can be applied to mixtures with host sands of different coefficients of uniformity, particle sizes and particle shapes over a wide range of polypropylene-type fiber contents (up to 2%).
iv. Under anisotropic stress path, the presence of fiber increased the influence of the stress ratio on the normalized modulus (Gmax,normalised = [Gmax (ani)/ F(eani)]/[Gmax (iso)/F(eiso)]). This observation is possibly attributed to the plastic strain history, but the effect becomes weaker at greater effective confining stresses.
v. Based on a comprehensive set of experimental data, new models for the prediction of normalized shear modulus of sand-fiber mixtures, as well as pure sand specimens, subjected to anisotropic stress path are developed, as a function of mean effective confining pressure, stress ratio, coefficient of uniformity of the host sand and fiber content. The damping ratio, in a normalized form, is correlated with the normalized shear modulus reduction.