Investigation of Moisture Variation of Backfill Soil in MSE Wall

Abstract

The use of mechanically stabilized earth (MSE) retaining wall has gained popularity as an alternative of conventional cast in place concrete walls. The construction of MSE wall is cost effective, requires less site preparation and technically more feasible. However, the performance of MSE wall strongly depends on the backfill soil condition. Backfill soil with high percentage of fine content can cause excessive movement or even failure due to their poor drainage behavior. This paper presents a study on the investigation of backfill soil condition of MSE wall located at state highway 342, Lancaster, Texas. The top of the wall has moved as much as 300 mm to 450 mm at some locations, in only five years after construction. Site investigation included soil test boring, installation of inclinometers and resistivity imaging (RI). The soil samples collected from backfill zone were classified as clayey sand (SC) according to Unified Soil Classification System (USCS). Laboratory testing conducted on the collected soil samples showed 29% to 39% of fine content in backfill soil. RI was performed twice during the investigation period to monitor the moisture condition within the backfill soil. Based on the RI, perched water zones were encountered in two locations near inclinometers. Moreover, increase in perched water zones were observed from March 2010 to July 2010. Moisture content of backfill soil was determined using RI along two profiles in the perched water zones. Increase in moisture content along profiles was observed during investigation period. The rate of wall movement also increased from 1 mm/month to 4 mm/month during this period.