Laboratory Investigation of Pullout Behavior of Open-Ended Pipe Helical Soil Nail in Frictional Soil

Abstract

In the present work, an experimental study has been conducted to investigate the pullout behavior of helical soil nails fabricated using a hollow pipe with an open end. The main objective of the study is to evaluate the contribution of soil plugging during torque installation and progressive pullout of openended helical soil nail (OPHN). The OPHN is installed in a model tank filled with cohesionless soil and subjected to pullout testing. Five different combinations of OPHN varying in shaft diameter (d), helix diameter (Dh), and the number of helices have been used. The test results show that with an increase in Dh/ d ratio and surcharge pressure, both installation torque and peak pullout capacity increases. For OPHN, pullout capacity is related to installation torque by a torque coefficient (Kt) varying from 28.12 to 53.3 m-1. The effect of soil plugging is examined in terms of plug length ratio depicting values from 0.19 to 0.28 and constituting 12% of total mobilized shaft friction. The results also depict that installation torque and pullout increase with increasing plug length which depends on ‘d’ and is independent of the number of helices. Smaller soil plug length corresponds to higher axial strains during the pullout of OPHN.