Enhancement of compaction grouting on a compaction-grouted soil nail in sand

The compaction grouting is an important factor in enhancing the performance of the newly developed compaction-grouted soil nail. Based on the self-developed large-scale model system, two series of pull-out tests with and without compaction grouting are carried out, and their results are compared to study the influences of compaction grouting on the enhancement of the pull-out force of the new soil nail. In addition, a hyperbolic model that can well describe the evolution of pull-out force with displacement is proposed. The study shows that: (1) The compaction grouting has significant influence on the pullout force within small pullout displacement, while it has small influence on the final pullout force. Moreover, when the soil conditions change, the compaction grouting (leading to soil densification) on the performance of soil nails depends on the grouting pressure rather than the diameter of the grout bulb. (2) The differences in soil responses caused by the compaction grouting, including vertical dilatation, the vertical and horizontal squeezing effects, are the main causes that lead to the difference in the increase rate of the pullout force of soil nails. (3) By introducing two parameters, the compression modulus and the ultimate pullout stress, a hyperbolic pullout model is proposed. After verification, the pullout forces can be calculated for the given diameter of grout bulb and pullout displacement.