A semi-analytical model for a compaction-grouted soil nail with double grout bulbs considering compaction effect in sand

Abstract

A soil nail with double grout bulbs has excellent pullout resistance, and the model for calculating the pullout resistance is an important reference for the design of soil nail with double grout bulbs. A modified hyperbolic model for a compaction-grouted soil nail with double grout bulbs was proposed based on energy equilibrium method, in which the compaction effect derived from the grouting was also considered. Then, the calculated pull-out force using the hyperbolic model was verified by the test results. Then, the difference in pull-out force under two typical failure patterns was discussed. Finally, parametric studies regarding different spacing/diameter ratio (Sd/D2), dry density, initial compression modulus and overburden pressure were conducted under the two failure patterns. The results show that the bulb resistances from the cylindric surface and the curved surface contribute most to the pull-out forces under the first failure pattern and the second failure pattern, respectively. The pull-out force of the back section is linearly increase with the Sd/D2 and it is larger under the second failure pattern than that under the first failure pattern. The dry density and the initial compression modulus influence the initial increase rate of the pull-out force, while the overburden pressure not only influences the mobilization rate of the pull-out force but also the ultimate pull-out force.