Pullout of soil nail with circular discs: A three-dimensional finite element analysis

An internal failure mode for a soil-nailed system consists of failure at nail heads, slope facing, nail strength, along grout-soil interface and pullout failure. A better understanding of pullout of soil nail thus becomes important to assess the stability of a soil-nailed system. In the present study, an investigation into the pullout behaviour of soil nail with circular discs along the shaft has been carried out by a three-dimensional finite element analysis using Abaqus/Explicit routine. A total of 67 simulations have been performed to accurately predict the pullout behaviour of soil nail. The soil nail under study has circular discs along its shaft varying in numbers from 1 to 4. The pullout of this soil nail in a pullout test box has been simulated with a constant overburden pressure of 20 kPa acting on the nail. The pullout load-displacement characteristics, stresses around soil nail and failure mechanism during pullout are studied. Variations of dimensionless factors such as normalised pullout load factor and bearing capacity factor have been obtained with different combinations of parameters in terms of relative disc spacing ratio, anchorage length ratio, embedment ratio, diameter ratio and displacement ratio. From the results of analyses, it is found that nail with more circular discs requires higher pullout load. There are critical relative disc spacing ratio and diameter ratio which significantly affect the pullout behaviour of nail.