Groutability of granular soils using sodium pyrophosphate modified bentonite suspensions

Abstract

Groutability of granular soils using sodium pyrophosphate (SPP) modified bentonite suspensions was studied to investigate its applicability in permeation grouting. While the relative grain size of the soil and the grout has been widely used to evaluate the groutability of granular soils with particulate grouts, such criteria do not account for the effect of chemical modifications of grouts such as the changes in their rheological properties. The modification of grouts may improve the depth of its penetration, and thus changing the groutability of the granular soils. For such cases, the rheological properties of grouts become crucial to evaluate groutability of soils. In this study, the rheological properties of bentonite suspensions were measured at various bentonite fractions (5%, 7.5%, 10%, and 12% by total mass of suspension) modified with 0%, 1%, 2%, 3%, and 4% SPP (by mass of dry bentonite), respectively. The small amounts of SPP effectively improved the mobility of the concentrated bentonite suspensions allowing the evaluation of change in groutability at different rheological properties but same concentrations. The modified bentonite suspensions were injected into the saturated sand columns prepared at various experimental conditions (effective particle size, relative density, and fines content) under two different constant pressures (35 and 140kPa). The results showed that the injected pore volumes increased with an increase of the apparent viscosity at equilibrium (high shear rates). A new groutability criterion for granular soils is proposed based on the rheological properties of the suspensions, relative density of the sand, relative grain size of the sand and bentonite, and injection pressure. The proposed groutability criterion provides a more accurate prediction of groutability in granular soils when using modified bentonite suspensions.