Interaction between Drilled Shaft and Mechanically Stabilized Earth (MSE) Wall

Drilled shafts under horizontal loads are being constructed within Mechanically Stabled Earth (MSE) walls in the reinforced zone especially in overpass bridges and traffic signs. The interaction between the drilled shafts and the MSE wall is not well known and not typically incorporated in the design. To better understand the interaction, a full scaled test was conducted in 2012 at Texas A&M University. The test was performed on an MSE wall with backfill material of clean sand and soil reinforcements of metal strips. Also a real project was instrumented during construction and data gathered for couple of months from this project. Numerical model was used for further investigation and it was calibrated by the test results and the data from monitoring the real site.

Main focus in this research was on the MSE walls with metal strips and a detailed study was performed on the friction mechanism of metal strips. Numerical modeling was used to better understand the friction factor and the relation between the depth of reinforcement and the maximum tension in the strip. Also some numerical simulations were performed to better understand the effect of number of bumps per foot on the metal strips on the friction factor. The other part of the numerical study was focused on the effect of the shape of the bumps on the strips. Accordingly different strips were modeled with different numbers of bumps and with different bump shapes.

Sensitivity analysis and parametric study were performed and 64 numerical cases were modeled to understand the effect of different parameters on the interaction between the MSE wall and the drilled shaft.

The data from different numerical simulations, the full-scale test and the monitoring of the real site were processed and a modification to the current guideline was proposed for the case where there is a horizontally drilled shaft in the reinforced zone of the MSE wall. One of the final results of this research is a design chart which can help the designer of MSE walls with laterally loaded drilled shaft in the reinforced zone of the wall, to take the additional pressure on the wall according to the drilled shaft into the final design.