Using Bentonite to Reduce Neat Cement Grout Losses in Soil Nail Wall Applications

Soil nail walls are effective earth retention systems that reinforce soil masses to mitigate and repair geotechnical hazards, such as slides. A critical component of these structures is the cementitious grout encapsulating the soil nails, which bond the nail to the surrounding earth. A recognized challenge in soil nail wall applications is grout loss into voids and fissures of the in-situ ground conditions. Grout overages, increased costs, and project delays can arise if a site experiences severe grout loss into soil formations. This research investigated the introduction of varying percentages of bentonite, a naturally occurring clay mineral, as an admixture in the neat cement grout to increase the viscosity and potentially reduce the potential losses of grout away from the soil nails. This experimental study consisted of laboratory and field components to assess the impacts of varying bentonite percentages on grout properties. Based on the results of the laboratory tests, a grout mix between 4 and 6% bentonite, by weight of cement, and between 0.5 and 0.6 w/c ratio are recommended for field applications. The findings indicate that the introduction of bentonite into the neat cement grout of soil nails successfully increased the viscosity of the grout mix while also maintaining the strength of the grout. While the field testing of this study could not conclusively measure grout loss reduction, the field results did show a bond capacity increase of the bentonite grout mix and supported the probability of reduced grout loss. Additional research is needed to validate these assertions further.