Liquefaction response of the sand reinforced with 3D printed geocells

Abstract

Geocells are one of the most widely used geosynthetics, owing to their three-dimensional interconnected cellular structure that allows immediate support to heavy loads and provides high lateral confinement and wider dispersion of stresses. Though the mechanical response of the geocell-reinforced soils under static and cyclic loading conditions is well understood and established, the liquefaction response of geocell-reinforced soils is not understood so far. In the context of an exponential increase in the number of geocell-reinforced soil structures in roads, foundations and retaining walls, it is extremely important to quantify the liquefaction resistance of geocell-reinforced sand to assess the flow failures and lateral spreading associated with these structures. In addition, quantification of post-liquefaction strength loss of geocell-reinforced sand is essential to design geocell-reinforced soil structures for long-term applications. In this context, this thesis aims to understand the liquefaction response of the geocell-reinforced sands through cyclic triaxial tests, shaking table model tests and numerical analysis and quantifies the post-liquefaction shear strength loss in these sands. The commercially available geocells have high tensile strength and large physical dimensions, making them unsuitable for small-scale studies. Hence the geocells used in this study were fabricated through 3D printing of polypropylene sheets and ultrasonically welding them into geocells of smaller dimensions and lower tensile strength. The fabrication of the geocells involved the selection of the optimum printing parameters and welding parameters based on the tensile strength tests and interface direct shear tests. Complimenting the ultrasonic welding technique with 3D printing technology helped in mimicking the true honeycomb shape and structural flexibility of the commercial geocells. The pre-liquefaction monotonic shear strength, liquefaction resistance and post-liquefaction shear strength were quantified through systematic static and strain controlled cyclic triaxial tests. The influence of the geocell on the pore water pressure progression, stress-strain response, modulus degradation and strain energy dissipation at the elemental scale is comprehensively investigated. In the next stage of this study, the liquefaction response of sand beds with a layer of interconnected geocells was studied through shaking table model tests. The effectiveness of the geocell layer in hampering the pore water pressure development, reducing the acceleration amplification and improving the cyclic resistance of the sand beds is established through these studies. To extend the understanding to field-scale sand beds, numerical modelling was carried out using Fast Lagrangian Analysis of Continuum (FLAC) simulations. The models were validated using shaking table model tests and parametric analyses were carried out to understand the liquefaction response of sand beds with variation in the properties and dimensions of geocells, placement conditions of the sand and the geocell infill sand relative density. Based on the experimental and numerical studies, specific insights into the liquefaction potential of geocell-reinforced studies are gained and the quantitative benefits of geocell reinforcement in reducing the likelihood of liquefaction in sands are established.