Pullout resistance factors for steel MSE reinforcements embedded in gravelly backfill

This paper presents results from a laboratory program of 287 pullout tests of galvanized steel reinforcements used in the construction of mechanically stabilized earth (MSE) walls. Results focus on the evaluation of pullout resistance factors for ribbed steel strip and welded steel grid reinforcement embedded in gravelly backfill. This project used Texas Tech University's large-scale MSE test box with dimensions of 3.6 × 3.6 × 1.2 m and an applied overburden capacity equivalent to 12 m of soil fill. The research design evaluated pullout resistance factors for both ribbed strip and welded grid reinforcements for a variety of independent variables, including overburden pressure, reinforcement length, grid bar size, and grid geometry including both transverse and longitudinal bar spacing. Appropriate statistical analyses were used to interpret the data within the context of published design guidance for inextensible MSE reinforcements. The results show that pullout resistance factors for both ribbed strips and welded grids in properly compacted gravelly backfill are significantly higher than those obtained for reinforcements embedded in sandy backfill, as well as default pullout resistance factors. In addition, the results obtained for welded grids indicate that transverse and longitudinal bar spacing, factors not considered in the current formulation, have significant influence on the pullout resistance capacity.