Grain Shape Effects on the Liquefaction Response of Geotextile-Reinforced Sands

Using low-cost polymeric geosynthetics has proven to be a sustainable solution for a wide range of geotechnical problems, including liquefaction and associated disasters. The grain shape of sand governs the sand-geosynthetic interactions and its macro-level mechanical behavior and is the key to understanding and obtaining performance-based designs for reinforced soil structures. This paper investigates the micromechanics behind the effects of grain shape on the liquefaction response of unreinforced and reinforced sand through strain-controlled consolidated, truly undrained cyclic simple shear tests on granular materials with the same grain size and different grain shapes varying from completely rounded to angular. A layer of nonwoven geotextile was used in tests on reinforced sand. Grain shape is characterized through microscopic image analysis carried out in MATLAB. A series of densification tests and interface shear tests are performed to complement the cyclic simple shear tests in understanding the mechanism of liquefaction. With the increase in particle angularity by 77 and 123 times, the liquefaction resistance of the reinforced sand in terms of the number of cycles increased by about 200% and 270%, respectively. Results showed that the rate of densification is significantly affected by the particle shape and inclusion of geotextile, with maximum retardation of 24% for angular particles. An increase in the angularity of the particles has two advantages for providing liquefaction resistance to the particles: first, by increasing interlocking to achieve a stable configuration, and second, by improving interface friction to prevent particle movement and mobilization of pore water pressure.