Lessons Learned from Settlement of Three Highway Embankment MSE Walls

Abstract

Three MSE walls were constructed along a two-lane rural highway where the use of non-standard on-site material as wall backfill initially appeared to be a great cost-savings measure with relatively low risk to the overall performance of the walls. The MSE walls ranged in maximum height from 8 to 11 meters and extended from 119 to 332 meters in length. Settlement of 76 to 152 millimeters was observed in the outbound roadway lane less than six months after construction. Longitudinal cracking appeared near the centerline of the roadway above the MSE walls, with voids up to 2 meters deep at spot locations. Roadway distress above the MSE walls was caused by settlement and piping of the wall backfill material. Several site-specific issues contributing to the MSE wall distress, including; (1) up to 45% fines in the wall backfill material, (2) rigid temporary shoring (soil nail walls) at the back of the more flexible MSE wall, and (3) an unlined ditch at the top of the wall, allowing surface water to flow through the clean gravel roadway base course to the back of the MSE wall. Three main lessons were learned from this case history. First, using non-standard on-site material as wall backfill ended up costing more than if imported fill was used, even though initial project costs were less and it appeared to be low risk to the wall performance. Secondly, temporary shoring systems need to be considered in conjunction with the design of MSE walls due to the differences in potential deformation between the two systems, which could lead to cracking at the interface of the two walls. Thirdly, prevention of surface water infiltration into the MSE wall system would have prevented piping of the wall backfill material and drainage improvements are relatively inexpensive costs compared to the overall cost of the entire MSE wall.