PULLOUT RESISTANCE OF MECHANICALLY STABILIZED EARTH REINFORCEMENTS EMBEDDED IN COARSE BACKFILL AND MEASURED IN A LARGE SCALE TEST SYSTEM

One of the two major components of an MSE wall design is the design of adequate soil reinforcement to ensure the internal stability of the walls. The soil reinforcement design is based on both the rupture capacity and the pullout capacity of the reinforcing elements. The pullout capacities of soil reinforcements are often found to be the more critical design criterion. The calculation of pullout capacities of reinforcement is based on AASHTO specifications which provide guidance on how to find the appropriate Pullout Resistance Factors (F*) given the reinforcement and backfill types. In an attempt to further economize the construction of MSE walls, the Texas Department of Transportation (TxDOT) initiated a research study to update these F* values to better suit TxDOT specified backfill materials which have superior performance characteristics in comparison to backfill materials on which the AASHTO guidelines have been based. As a part of this TxDOT project, this study carried out testing on the pullout resistance of Ribbed Steel Strip, Welded Steel Grid, and Smooth Steel Bar type reinforcements in TxDOT specified coarse (Type A) backfill. The research objective was to understand the relationship between F* and variables such as vertical overburden stress, reinforcement dimensions and reinforcement orientation. Testing of these variables required a large scale test system which was capable of accommodating multiple full-sized reinforcements and simulating field conditions as closely as possible. The collected data was analyzed using statistical tools, and mathematical models were developed to fit the observed trends. These models are intended to be used to provide additional guidance for MSE walls built by TxDOT in the future.