Frictional Resistance of Closely Spaced Steel Reinforcement Strips Used in MSE Walls: Fid-Bau Portal

Frictional Resistance of Closely Spaced Steel Reinforcement Strips Used in MSE Walls

Strahler, Andrew W. / Walters, James J. / Stuedlein, Armin W.

Frictional resistance between soil and steel reinforcements develops as a result of relative displacement at the soil-reinforcement interface and is typically characterized using interface shear or reinforcement pullout tests. The soil-reinforcement interaction between uniformly-graded soils and metal reinforcements has been well-characterized. However, the interface response of well-graded gravelly soils and ribbed steel strips is primarily based on lower-bound estimates of pullout resistance using databases of single isolated reinforcement pullout tests. Increases in horizontal stresses that develop in tall mechanically stabilized earth (MSE) walls are often accounted for in design by reducing the reinforcement spacing; however, the effect of possible frictional interference between closely spaced inextensible reinforcements has not been explored. Two reinforcement pullout apparatuses have been developed to study the soil-reinforcement interaction and effect of reinforcement proximity in a well-graded sandy gravel. A single strip pullout apparatus was developed to establish the baseline frictional resistance, comparable to typically-conducted pullout tests. The assessment of reinforcement strip interaction effects possible in closely spaced reinforcements was evaluated using a multistrip pullout apparatus. The effects of passive resistance at the front facing that alters the load-displacement response and contribute to epistemic uncertainty were mitigated using a well-characterized, soft boundary condition. Generally, the available resistance was observed to increase with increases in the localized stiffness, whereas the secant stiffness of the resistance-displacement response reduced with increases in localized stiffness. Current pullout resistance factor models are shown to be conservative and biased, and recently proposed calibrated exponential models more accurately capture the measured responses. Fitted isolated and confined strip models presented in this paper should help practitioners estimate the frictional resistance of ribbed steel strips in sandy gravel soils and incorporate increases resulting from closely spaced reinforcements into design methodologies and numerical simulations.