Mechanical responses of sands treated with soft viscoelastic gelatin

Abstract

Geotechnical engineering recently considers the contribution of viscoelastic material on particulate media as a particle binding material with societal demands for environmentally friendly construction materials and techniques. Until now, cement, lime, sodium silicate, acryl, and acrylamide polyurethane have been used as materials to improve the engineering properties of soils. Various efforts have characterized and modeled mechanical behaviors of cemented soils associated with chemical grout materials of high brittleness. However, injection of these chemical grouts is often problematic due to water pollution and environmental regulations. In general, mechanical responses of biopolymers are characterized as viscoelastic behaviors associated with small stiffness and low strength. By contrast to brittle, cemented soils, the impact of soft viscoelastic inclusions, such as gel-like biopolymers, on mechanical responses of treated soils remains poorly understood. Therefore, this dissertation is aimed at obtaining a better understanding of the effect of soft viscoelastic material on load-deformation behavior. First, in Chapter 2, gelatin extracted from bovine-hide was selected as analogue material, and various viscoelastic behaviors are made by changing the concentration of gelatin and quantified. In Chapter 3, A series of the consolidated-undrained (CU) compression tests are conducted using loose and contractive sands treated with gelatin to obtain stress-strain responses and monitor variations in S-wave velocity (VS) during undrained loading. The results of stress-strain curves, shear wave velocity variations, and effective stress paths reveal that the inclusion of a viscoelastic biopolymer restrains the contractive behavior associated with post-peak softening but increases the undrained shear strength of contractive loose sands. In chapter 4, a simplified resonant column apparatus is developed to measure the dynamic properties of sands in low frequency. In Chapter 5, The resonant column device developed in chapter 4 measures the dynamic properties during gelation. The shear wave velocity is constant and the damping ratio increases during gelation. As the gelatin concentration increased, the damping ratio increases due to the viscose friction of gelatin. The normalized shear modulus curve is located at the upper part and the lower part of the normalized damping ratio curve is positioned at the lower part in intermediate strain. In Chapter 6, effect of viscoelastic inclusion on the liquefaction resistance of sands is investigated by conducting the cyclic simple shear test. The biopolymer-treated sand specimens with low concentration of viscoelastic material showed weak liquefaction resistance than the biopolymer-free sand specimens with similar relative density due to lubrication effect between sand particles. However, when a certain gelatin concentration is secured, liquefaction does not occur with a decrease in shear strain during cyclic loads. Although large deformations occur at low concentrations, the gelatin prevents the volume contraction of sands, so that the excess pore water pressure is less than the initial vertical stress, and the effective stress does not decrease to zero.