Dynamic Rheological Properties of Sodium Pyrophosphate-Modified Bentonite Suspensions for Liquefaction Mitigation

Abstract

AbstractThe delivery of plastic fines such as bentonite into loose saturated granular soil deposits is an effective method for mitigating the liquefaction phenomenon. While the bentonite should be injected into the deposits in the form of a concentrated suspension, such application is limited in practice because of the low mobility of the suspension. The initial mobility of the bentonite suspension should be managed in order to increase the penetration depth. On the other hand, the suspension needs to maintain its thixotropic nature to improve the resistance of the treated soils under cyclic loading over time. The objective of the present study was to investigate the dynamic rheological properties of the bentonite suspensions modified with an ionic additive, sodium pyrophosphate (SPP), to evaluate a possible application of the modified suspensions in mitigation of liquefaction. In the present study, the storage and loss modulus of SPP-modified bentonite suspensions were measured using a strain-sweep (oscillatory shear) technique. Bentonite suspensions with clay contents of 5, 7.5, 10, and 12 wt.% (by total weight of suspension) were tested at various SPP concentrations (0 to 4 wt.% by weight of dry bentonite). The time-dependent behavior of the suspensions was evaluated with a critical storage modulus at various resting times (0 to 480 h). The results showed that the initial critical storage modulus decreased significantly with increasing SPP concentrations, but the reduced critical storage modulus increased gradually with resting times. This initial reduction in critical storage modulus is attributed to a reduction of the inter-aggregated 3-D networks due to the presence of SPP; the amount of 3-D network formed in a suspension governs the critical storage modulus. With time, the networks are formed gradually, resulting in recovery of critical storage modulus. The normalized modulus was degraded more slowly in the modified suspensions than in the unmodified suspensions, which is a desirable property of the suspensions for mitigation of liquefaction.