Effects of Backfill Soil on Excessive Movement of MSE Wall

The use of mechanically stabilized earth (MSE) retaining walls has gained popularity as an alternative to conventional cast-in-place concrete walls. The construction of MSE walls is cost effective, requires less site preparation, and is technically more feasible compared with conventional concrete retaining walls. However, use of backfill with high fine content and poor drainage behavior can cause excessive wall movement or even failure. The current paper presents the case study of a MSE wall located at State Highway 342 in Lancaster, Texas. The top of the MSE wall has moved as much as 300–450 mm only 5 years after construction. An extensive site and laboratory investigation testing program was conducted to determine the possible causes of the MSE wall movement. The site investigation included soil test boring and resistivity imaging (RI). Perched water zones were identified at a few locations in the backfill area using RI. The bulging of the MSE wall facings was observed where the perched water zones were located. Laboratory testing of the collected soil samples was conducted to determine the characteristics of the backfill soil. The test results indicated the backfill soil was clayey sand according to the Unified Soil Classification System. Based on the test results and analyses, it was determined that the presence of high fine content may have caused the excessive movement of the MSE wall. The movement of the MSE wall was also modeled using the finite-element program PLAXIS, and is presented in this paper. The actual movement of the MSE wall and the obtained movement from the model were in good agreement.