Fiber-reinforced internally unstable soil against suffusion failure

Abstract

Gap-graded soil, classified as internally unstable soil, is susceptible to hydraulic failure due to the migration and erosion of fine particles through the coarse particle matrix at a relatively low hydraulic gradient. This internal erosion process, known as suffusion, is a hazardous phenomenon that can undermine the strength and stability of earth structures or their foundation. In this study, a series of seepage tests was conducted to investigate the hydraulic responses of fiber-reinforced gap-graded soil (FRS) and to evaluate the effectiveness of adding fiber to improve the internal erosion resistance of soil against suffusion. The respective influences of fiber parameters (i.e., fiber content and length) on the failure mode, hydraulic conductivity (k), Forchheimer coefficients (κ and β), and critical hydraulic gradient (icr) of FRS were quantitatively assessed. Soil-fiber interactions and improvement mechanisms, including fiber netting effect and vertical reinforcing effect, are discussed. Experimental results demonstrated that the inclusion of a small number of fibers can effectively improve the internal erosion resistance of gap-graded soils against suffusion. Hydraulic conductivity decreases and the Forchheimer coefficient β increases as fiber content increases. With an increase in the total number of fibers (i.e., high fiber content and short fiber length), the critical hydraulic gradient increases at various stages of the erosion process (determined at the onset of internal erosion, at the transition of flow from laminar to turbulent conditions, and at hydraulic failure). When the normalized number of fibers exceeds 1%, the failure mode shifts from suffusion to general piping, which resembles the failure mode of internally stable soil (i.e., uniform soil).