PULL-OUT RESISTANCE MECHANISM OF A SOIL NAIL REINFORCEMENT IN DILATIVE SOILS

S. Q. LUO S A TAN and K. Y. YONG

ABSTRACT An analytical model for the pull-out resistance of a rigid soil nail reinforcement in dilative soils is described in this paper. This model can be used to describe the pull-out response of a soil nail or any longitudinal strip reinforcement in dilative soils. An expression of the normal pressure on the shaft of the reinforcement as a function of soil dilation is derived. Based on the assumption that soil is an elastic medium and the soil nail is a rigid rod, an equation to calculate the pull-out resistance of the soil nail is obtained. The equation shows that apparent friction coefficient decreases with the increase of the overburden pressure or applied normal confining pressure around the soil nail. The analytical predictions and experimental results for two published test cases are compared. The first case involves pull-out tests on circular steel bars, and the second case is pull-out tests on rectangular steel strip reinforcements in dense sand. The agreement among the analytical predictions and experimental pull-out resistance results for increasing overburden pressure are good, showing that the apparent coefficient of friction decreases with increasing confining pressure. Thus the analytical model provides a theoretical basis to reasonably predict the pull-out resistance of a soil nail reinforcement in dilative soils.

Key words: dilatancy, pull-out mechanism, shear resistance, soil nail (IGC: E12)