Distinguished Speaker Seminar:
Monday, October 2 at 4 p.m.
350 DuPont Hall
“Lessons Learned from Failed MSE Walls”
During the past four decades, Mechanically Stabilized Earth (MSE) walls have gained acceptance in major critical applications. Generally, MSE walls are economical, aesthetically pleasing, and, if properly designed and constructed, safe. However, as is the typical case with fine-tuned efficient structures, details are critically important since structural redundancy could be limited. Forensic studies of several case histories of failed MSE walls are presented. These walls use metallic or geosynthetic reinforcement and facing made of steel mesh, small concrete units, or large reinforced concrete panels. The cases include walls with a simple or complex (multitiered) geometry. One failed a year after construction, and one was a 10 km long seawall. Four cases were in the US, one in Jordan, and the seawall case was in Sydney, Australia. Forensic studies are discussed. It is concluded that the likely reason for the failure of one wall was trivial design omission while others failed due to poor construction combined with oversight in design. In one case no reinforcement was placed in sectors next to a corner, a detail that is hard to accomplish. In another case, the top geogrid layer was omitted at a critical location. In the seawall case, the contractor did not pay attention to details related to a secondary and inexpensive component of the structure, a nonwoven geotextile filter behind the facing, leading to a progressive loss of backfill. One design error relates to the failure to capture the critical conditions as required in reinforced slope stability analysis. In one case, typical to other known failures, the geogrid was down-dragged by the compressing backfill leading to its tear at the connection due to the sharp edge of the concrete block facing. Not surprisingly, it is concluded that the cost of repair is far more expensive than the savings due to skimped design and construction.