Material Characterization and Design Recommendations for Mechanically Stabilized Earth Retaining Walls

Since its appearance in 1970s, mechanically stabilized earth (MSE) walls have become a majority among all types of retaining walls due to their economics and satisfactory performance. The Texas Department of Transportation has primarily adopted the Federal Highway Administration and American Association of State Highway and Transportation Officials (AASHTO) guidelines for design of MSE walls.

The research addresses three main issues expressed by TxDOT in their design and material selection process. The literature review in this research addresses the current practice and guidelines adopted by TxDOT as well as other Department of Transportations.

The first part of this dissertation explains the laboratory test performed on backfill materials used in Texas. The material classification was carried out according to TxDOT specifications and the laboratory test consist of performing state-of-the-art large scale triaxial test on large particles to evaluate engineering properties of backfill materials and a consolidated undrained test on a backfill material with higher amount fine particles present in that soil.

The second part of this addresses the issues on global stability and failure modes associated with it. A Fast Lagrangian Analysis of Continua (FLAC) program was used to asseses possible failure modes for MSE walls with different geometries and soil parameters for retained and foundation soils.

Finally, a parametric study was performed for sliding analysis using AASTHO recommended design parameters and comparing them with modified design parameters calculated from FLAC simulations for different geometries and soil parameters. Similarly, a parametric study was performed to address bearing capacity issues for MSE walls and justification of AASHTO recommendation with German code (EBGEO) for MSE walls.

The outcome this research shows that, the friction angle (?) for the backfill materials used in Texas is higher than AASHTO recommended values for large particles size type backfills. From FLAC simulations it shows that the global failure mechanism for MSE walls is dependent on type of soil properties used as retained and foundation soils. The parametric study shows that a modified parameters can be used for sliding analysis and for bearing capacity analysis a combination of Vesic?s and German code can be used.