Assessing Liquefaction Resistance of Fiber-Reinforced Sand Using a New Pore Pressure Ratio

Mixing discrete flexible fibers into sand is a reinforcement technology that increases the sand’s strength as well as ability to resist liquefaction. This study demonstrates the mechanisms by which the applied loads are distributed across and shared by a sand’s skeleton, the fibers, and the pore water in drained and undrained triaxial compression tests. It is shown how the effective stress on the sand skeleton may be quantified by invoking the rule of mixtures and separate constitutive laws for the fibers and sand skeleton. It is also shown how the fibers alter the load paths experienced by the sand skeleton. Most notably it is shown how the fibers prevent liquefaction and that the conventionally defined pore water pressure ratio may incorrectly indicate otherwise. Alternate and more suitable pore water pressure ratios are introduced, accounting for the transversely isotropic orientation distribution of fibers that prevails in most fiber-reinforced soils, that gives an accurate indication of how far away the reinforced sand skeleton is from a liquefied state. The new pore pressure ratios, which are dependent on the direction of the principal stresses and account for the fiber orientations, are for use in any situation when the potential liquefaction of fiber-reinforced sand is a concern. Use of the conventional pore pressure ratio, which until now has been the only one employed in the literature, may make the fiber-reinforcement technology appear less effective at suppressing liquefaction than it actually is. This may, incorrectly, hinder its uptake in industry.