Framework for Determining the Pullout Resistance of Inextensible 2-Wire Soil-Reinforcing Elements Embedded in Sand

Abstract

Mechanically Stabilized Earth (MSE) has been successfully used as a commercial retaining structure since its development in 1963 by Henry Vidal (Schlosser 1990). MSE is a ground improvement system that consists of soil-reinforcing, compacted backfill, and a facing. The initial soil-reinforcing developed for commercial use by Vidal consisted of a smooth steel strip. Since then, a diverse range of soil-reinforcing has been developed, including extensible and inextensible reinforcing. The various geometric configurations of soil-reinforcing have included wide width and narrow width elements comprising planar strips, planar grids, co-planar strips, co-planar grids, and wide sheets. General specifications categorize inextensible soil-reinforcing into metallic linear strips, metallic welded-wire mesh, and metallic bar mats, while extensible soil-reinforcing is categorized into geogrids and polymer strips. A soil-reinforcing element that consists of metallic welded wire, also known as a bar-mat, with only two longitudinal wires and a series of transverse wires is currently being utilized as soil-reinforcing in MSE systems. The 2-Wire soil-reinforcing element is a linear strip that resembles a ladder. The 2-Wire configuration of inextensible soil-reinforcing is not technically categorized or defined within the general specification. In other words this raises the question, is the 2-Wire element a linear strip, a welded-wire system, a bar-mat system, or should it be uniquely identified? The semi-empirical equations used to determine the pullout resistance of an inextensible grid system include a pullout coefficient, also known as a bearing resistance factor. The bearing resistance factor is soil-reinforcing dependent. For inextensible grid systems, it has been empirically established that the bearing resistance factor is a function of the transverse wire size and the transverse wire spacing. The spacing of the longitudinal wire is not considered in the equation. As an illustration, a grid system of a given width, for example 1220 mm, with 300 mm spaced longitudinal wires, is assumed to act in the same manner as a grid system with 50 mm spaced longitudinal wires. The objective of this research is to develop a bearing resistance factor for commonly used 2-Wire soil-reinforcing elements. This will be accomplished by performing pullout test on 2-Wire elements utilizing a state-of-practice pullout program.