Experimental investigation of pullout behaviour of open-ended pipe helical soil nail in frictional soil

Abstract

ABSTRACT The presented work examines the pullout response of open-ended pipe helical soil nails in cohesionless soil. Assessments are made on the basis of installation and displacement controlled pullout test. The nails were designed to isolate the soil plug effect, inner skin friction, and bearing resistance contribution to nail capacity. The findings suggest that as pipe diameter and number of helices increases, the installation torque and pullout stress of open-ended pipe also increases. The plug length increases with increase in penetration depth ratio up to five and thereby becomes constant. At qual to five, the plug length is 10% and 14.2% of total and effective length of nail. The empirical factor (Kt) during tension and compressive loading varies from 28.12m-1 to 53.3m-1 and 27m-1 to 55m-1 respectively for different nail specimens. The experimental Kt values are found in good agreement (Regression value R2 = 0.997 in tension and R2 = 0.994 in compression) with theoretical Kt. The mean prediction ratio of torque factor in tension and compression was 1.07 and 1.03 respectively. It is concluded that pullout strength is directly proportional to the plug length due to increased adhesion and friction between soil - open - ended helical soil nail interfaces.