Mechanical Behavior of Ultrafine Cement-Grouted Sands under Unsaturated Conditions

Cementitous grout is often used in permeation grouting applications, such as in seepage cutoff. However, ordinary Portland cement can be ineffective for permeation grouting of fine-grained sands or in sands with significant amounts of fines. Ultrafine cement grout thus becomes a viable alternative material for grout applications in these types of soils. While a major benefit of ultrafine grout is its penetration ability into the soils with relatively low hydraulic conductivity, the strength of the ultrafine grouted soil mass is not thoroughly discussed in literature. This study investigated initial conditions that could affect grout application effectiveness. An apparatus was developed so that a controlled volume of grout could be injected into a soil specimen. This study found that increases in water-to-cement ratio have a significant effect on the unconfined compressive strength of the neat grout. Grout penetration rates through the samples decreased as matric suction increased. The observed grout penetration rates were observed to be an inverse function of the unsaturated hydraulic conductivity. Also, the strength of the grouted sand was observed to increase as the matric suction increased. The results of this study suggest that knowledge of matric suction may be useful for estimating injection penetration rates and strength of ultrafine grouted sand.