Groutability of Granular Soils Using Bentonite Grout Based on Filtration Model

This paper describes an experimental and a numerical study on the groutability of granular soils using sodium pyrophosphate (SPP)-modified bentonite grout to investigate its possible application in permeation grouting. While the groutability criteria based on the relative grain size of the soil and the grout have been widely used for particulate grouts, such criteria do not account for the change in groutability of soils due to chemical modifications of the grouts. Moreover, the bentonite grout has different physicochemical properties such as particle size and pH from those in the cement-based grout, resulting in different filtration character, and thus different groutability of soils. Therefore, it is difficult to apply the existing criteria developed for the cement-based grout to the bentonite grout. In this study, the apparent viscosities of various bentonite grouts (5, 7.5, 10, and 12 %, wt/wt %) with 0-4 % SPP were measured using an advanced rheometer. The grouts were injected through sand columns having different effective particle sizes (0.2, 0.28, and 0.31 mm) under two constant pressures (35 and 140 kPa). A 1D filtration model was utilized to simulate the grout flow through the sand columns. A lumped parameter that accounts for physicochemical properties of bentonite grouts was evaluated by calibrating the model with the experimental data. The results showed that the apparent viscosity of 7.5, 10, and 12 % bentonite suspensions decreased approximately 50 % with the SPP concentrations of 1, 3, and 4 %, respectively. Moreover, the lumped parameter increased with the decrease in the effective grain size of the sand and decreased with the decrease in the apparent viscosity of the grout. This implies that filtration during the grout flow was reduced with the SPP modification. The parameter also decreased with the increase in injection pressure and relative density. A new groutability criterion for bentonite grout was proposed based on the relationship between the injected pore volume and the lumped parameter. The criterion was compared to the existing criteria, leading to more accurate prediction of groutability in the tested sands. The proposed groutability criterion will be beneficial to design grouting works by more accurately predicting the groutability of granular soils for SPP modified bentonite grouts than the existing criteria.