Post-Grouting Stability of Bentonite Suspensions within Sand Pores: Fid-Bau Portal

Post-Grouting Stability of Bentonite Suspensions within Sand Pores

El Mohtar, Chadi / ElKhattab, May / Sangroya, Ritika

Permeation grouting can be an effective way to deliver bentonite into porous media to control ground water flow. Bentonite slurries can be permeated into the porous media to reduce the hydraulic conductivity of the original soil. While some work has been done on the change in hydraulic conductivity of the soils when introducing bentonite, the stability of the bentonite within the pore space has not been significantly investigated. The current paper presents a study on the post-grouting stability of bentonite grouts within a porous media. The performance of bentonite grout in permeated sands was investigated by studying the rheological properties of bentonite suspensions (particularly, yield stress) and stability of the ground under in situ hydraulic gradients. The rheological parameters of bentonite suspensions were measured at various bentonite concentrations (ranging from 6 to 16% bentonite to total weight) with and without sodium pyrophosphate (SPP) modifications (SPP percentage ranged from 1 to 11% by dry weight of bentonite). SPP is an ionic additive used to temporary control the rheological properties of the bentonite grouts. The stability of bentonite grout was inspected by studying the hydraulic conductivity of sand permeated with bentonite suspensions under increasing hydraulic gradients; when washing out occurs, it results in an increase in hydraulic conductivity. The critical hydraulic gradient at which washing out of bentonite suspensions is initiated was examined. Accordingly, a relation between the yield stress of bentonite suspensions and the critical hydraulic conductivity is developed.