Cyclic behavior and pore pressure generation in sands with laponite, a super-plastic nanoparticle

Abstract

The paper examines the effect of the presence of small percentages (1–5%) by dry mass of the sand of laponite – a synthetic nanoclay with plasticity index exceeding 1000% – on the cyclic response of sand with relative density in the 15–25% range. The work is based on cyclic triaxial tests performed on specimens prepared pluviating sand and laponite under dry conditions and then permeated with water. 1% laponite impacts all stages of the cyclic tests, from the response during the first loading cycle to liquefaction, increasing the cyclic resistance. Further benefits are observed with a longer pre-shear aging period or higher dosages (3–5%) of laponite.The observed behavior is associated with reduced mobility of the sand particles during cyclic loading, which can be ascribed to two mechanisms: (1) bonding/bridging at the particle contacts due to the charged laponite fines which are attracted to the sand grains; and (2) formation of a pore fluid with solid like properties. The first appears to control the behavior with 1% laponite, while it is proposed that the second is responsible for the response with higher dosages of laponite.The results presented provide new insight into the effects of high plastic fines on the cyclic response of sands, the “extreme” effects of the plasticity of the fines, and are significant in light of the possible use of laponite for liquefaction mitigation, an idea first put forth by the authors.