Long-Term Performance Evaluation of Reinforced Embankment Test Sections Over Extremely, Soft Compressible Soil: A Case Study in Louisiana

Constructing roads across the swamps of south Louisiana has created unique challenges. Soft saturated subgrades often exist, causing embankment stability and long-term settlement issues that must be considered in the geotechnical design of these embankments. Historically, sand embankments constructed over soft soil required wide stability berms to prevent deep-seated failures (no improvement with depth). Although geosynthetic reinforcements have allowed sand embankment construction directly on the natural ground without muck excavations, the weight has caused serious settlement problems. Some roadways have settled to the extent that under extreme flood conditions, the roadway was partially underwater, restricting hurricane evacuation operations. Roadway undulation caused by differential settlement also produced a "roller coaster" ride. The objective of this study is to evaluate the long-term performance of test sections with geosynthetics and lightweight fill material. During this study, the long-term performance of five embankment test sections constructed on soft compressible soils after construction was investigated. It involved the design, construction, and long-term monitoring of these test sections on a relocation project for U.S. 90, a major arterial road connecting New Orleans with Lafayette through southern Louisiana (eventually I-49), over a period of time extending from 1990 to 1999. This evaluation compiled both past and present data into a result, providing insights into the long-term performance and stability of these embankments.