A new capillary barrier system for retaining wall backfilled with fine-grained soil

Abstract

Retaining wall back-filled with fine-grained soil such as silt is vulnerable to failure due to its low water permeability under heavy rainfall. Based on unsaturated soil mechanics, a new capillary barrier concept is proposed to form a back-filled retaining wall to reduce water infiltration under rainfall. The capillary barrier retaining system consists of a fine-grained soil (silt), a nonwoven geotextile, and a coarse-grained soil (sand). The effectiveness of the proposed retaining system is analyzed using the finite element method to investigate its corresponding hydraulic response and stability subject to rainfall with 100-year return period. In addition, a numerical parametric study is conducted to reveal the influence of different properties of the nonwoven geotextile on the capillary barrier retaining system. The properties considered include the saturated permeability coefficient ks, the inverse of air-entry value ɑ, and the pore size distribution parameter n. It is found that high matric suction can be maintained within the silt backfill under the imposed rainfall and hence the factor of safety of the retaining system remains almost unchanged as compared with its initial conditions. The saturated permeability coefficient ks of the nonwoven geotextile is found to have a significant influence on the proposed capillary barrier retaining system. The lower ks is, the smaller the rate of increase in the volumetric water content of the nonwoven geotextile and hence the more stable the retaining wall.