Liquefaction Mitigation Using Bentonite Suspensions

Abstract

Ottawa sand specimens premixed with 0, 3, and 5% bentonite by dry mass of sand were tested under undrained static and cyclic loading to investigate the effects of bentonite on the static and cyclic shear strength of the sand. The results show that allowing the bentonite to hydrate within the sand pore space increases the cyclic resistance of the sand. For the same skeleton relative density and cyclic stress ratio, cyclic tests on specimens with sufficient hydration times showed a significant increase in the number of cycles required for liquefaction compared with clean sand. When the specimens were allowed an extended postconsolidation aging period, the cyclic resistance increased further. Resonant column and cyclic triaxial tests showed that this is a result of the delay in the generation of excess pore pressure in the presence of the bentonite suspension in the pore space. The improvement in cyclic behavior does not occur at the expense of the static resistance of the soil under working loads because undrained static triaxial tests on specimens with bentonite showed only a minor decrease in the small-strain internal friction angle compared with the clean sand, while the critical-state internal friction angle remained unchanged. To address the need to deliver the bentonite suspension in a sand deposit, a method for engineering the rheology of concentrated bentonite suspensions through the addition of sodium pyrophosphate (SPP) was developed. With the addition of 0.5% SPP by mass of clay, the viscosity of concentrated (10%) bentonite dispersions dropped to a value that allowed delivery of the bentonite into the sand matrix through permeation. Over time, the bentonite suspension recovered the thixotropic properties that ensured its effectiveness in mitigating liquefaction. As a result, sand specimens permeated with 10% bentonite suspensions showed a large increase in liquefaction resistance. Changes in the rheological properties of the pore fluid with time also explain the increase with aging of the cyclic resistance of the sand-bentonite specimens.

Laponita: una nanotecnología que retarda la licuefacción

“…La Figura 3 también muestra que, después del tiempo de gelificación, las dos suspensiones de Laponita son reológicamente equivalentes (en términos de G') a la suspensión con 10% de Bentonita. Esto es significativo ya que demuestra que una suspensión con 10% de Bentonita dentro de los poros de una arena, tiene éxito en la prevención de la licuefacción (El Mohtar et al, 2013.…”

“…Se debe tener en cuenta que 72 horas corresponde al tiempo cuando el módulo de corte de la suspensión con 3% de Laponita alcanza un valor relativamente constante, indicador que la gelificación de la suspensión de Laponita está completa (Figura 3). Además, a las 72 horas el módulo corte de la suspensión de Laponita es comparable a la de la suspensión con 10% de Bentonita, porcentaje que ha demostrado ser eficaz en el aumento de la resistencia de licuefacción de la arena (El Mohtar et al, 2013). El corte cíclico se realiza con una frecuencia de carga de 1 Hz.…”

“…Esto se ha intentado, en particular, en terrenos cercanos a estructuras civiles (Gallagher y Mitchell, 2002), donde las soluciones de mejoramiento de suelos más tradicionales, basadas en la densificación, no son viables. En este contexto, el reciente método basado en la modificación del fluido intersticial de la arena, reemplazando el agua en los poros del material granular por una suspensión concentrada de Bentonita, ha demostrado promisorios resultados (El Mohtar et al, 2013.…”

“…Figura 1: Influencia del contenido de finos en la licuefacción de arenas (Youd et al, 2001) El positivo efecto que los finos de alta plasticidad, particularmente la Bentonita, tienen en la resistencia a la licuefacción de arenas ha sido documentado por El Mohtar et al (2013Mohtar et al ( , 2014, con ensayos triaxiales cíclicos, demostrando que 3% de Bentonita, por peso seco de arena, aumenta el número de ciclos para llegar a la licuefacción. Este aumento es, al menos, un orden de magnitud, en relación a muestras de arena seca, a una misma densidad relativa.…”

Transferring innovative research into practical wisdom: the case of permeation grouting

“…A significant amount of research (at laboratory scale) has been performed in recent years on the use of chemical and suspension grouts for ground improvement [10,11,13,16,21,22,27,28,33]; however, field implementation has always been hindered by the in situ soil heterogeneity and discontinuities. Despite the complexity of the science behind permeation grouting, practitioners often reference in situ heterogeneity and variability to dismiss the need for a more systematic design approach.…”