Seismic analysis of Bored and Driven Soil Nailed Structures

Abstract

Soil nails serve as passive reinforcement components inserted horizontally into the ground to stabilize unstable soil masses and various subterranean or surface excavations. There are different types of soil nailing techniques, categorized based on their installation methods. In the case of driven nails, they are directly pushed into the structure during excavation. On the other hand, drilled and grout-type soil nails involve initially drilling a hole in the excavated soil face, followed by the installation of nails, which are subsequently filled with grout at low pressure. The design process of the soil nail structure hinges on upon its limit state of safety and serviceability. Soil nailed wall are designed based on two main methods. The first is the limit equilibrium method, and the other method is by using finite element analysis. In this study, we discussed the effects of 2D and 3D analyses of soil nailed structures and the differences in the outputs given by those analysis. The results of the 2D and 3D analysis in in various outputs in which the design of soil nailed walls depends upon like the global factor of safety, horizontal displacement at the top of the soil nailed wall, axial tension in nail, skin friction developed in the various construction stages is found out using a the PLAXIS 3D software. Further seismic inputs of Barpak and Kobe earthquake were used to study the dynamic behavior of the soil nailed structure. Results show that for both drill-grout nails and driven nails maximum displacement predicted by 2D analysis is more compared to 3D and more prominent difference was seen in driven nails compared to drill-grout nail. The maximum axial forces were found to be maximum at soil nails installed at a depth of about 2/3H from the top of the wall in both drill-grout nails and driven nails. Maximum displacement decreases as the L/H ratio increases for static loadings whereas in dynamic loadings L/H ratio seems to have little contribution for controlling displacement at lower values (less than 1). Maximum axial force developed in the soil nail decreases with the increase in magnitude of earthquake loading.