Pullout behavior of welded grid reinforcements embedded in coarse granular backfill

This paper describes a research program that conducted 214 pullout tests on welded steel grid reinforcements embedded in gravelly backfill. The pullout testing was conducted using Texas Tech University's large-scale MSE test box with dimensions of 3.6m x 3.6m x1.2m (12ft x 12ft x 4ft) and an applied overburden capacity of 12m (40ft) of backfill. This test box facilitates pullout testing at a scale not unlike typical field construction. The research design evaluated pullout resistance factors for welded grid reinforcements with varying reinforcement length, grid wire size, and grid geometry, including both transverse and longitudinal wire spacing. The grid reinforcement were tested under overburden fill depths ranging from 1.5m (5ft) to 12m (40ft). The results show that pullout resistance factors for welded grids embedded in gravelly backfill are much higher than the default pullout resistance factors provided by AASHTO. The data also show that the deformation of grid reinforcement under pullout forces play an important role in the development of pullout resistance. Moreover, the results show that such deformation contributes to additional stresses at the welded joints between longitudinal and transverse bars, which in turn may impair the integrity of the reinforcement.