A data base, statistics and recommendations regarding 171 failed geosynthetic reinforced mechanically stabilized earth (MSE) walls

摘要

Following the introduction of mechanically stabilized earth walls with metallic reinforcement in 1966, polymeric reinforced structures (both geotextile and geogrid) followed shortly thereafter. A major item that accompanied this change in reinforcement type was the nature of the backfill soil. Corrosion of metallic reinforcement was no longer an issue with polymer-related geosynthetics and thus locally available fine-grained soils were generally used in place of quarried coarse-grained gravel soil. The cost savings are obvious as are the implications for concerns over inadequate performance. While failures have occurred in both types of reinforced walls, this paper focuses only on geosynthetic reinforced walls. This data base of 171 failed mechanically stabilized earth (MSE) walls with geosynthetic reinforcement includes 44 cases of excessive deformation and 127 cases of collapse of at least part of the wall. The large majority are located in North America and in the USA in particular. The main statistical findings are as follows: 1. 96% were private (as opposed to public) financed walls 2. 78% were located in North America 3. 71% were masonry block faced 4. 65% were 4-12 m high 5. 91% were geogrid reinforced; the other 9% were geotextile reinforced 6. 86% failed in less than four years after their construction 7. 61% used silt and/or clay backfill in the reinforced soil zone 8. 72% had poor-to-moderate compaction 9. 98% were caused by improper design or construction (incidentally, none (0%) were caused by geosynthetic manufacturing failures) 10. 60% were caused by internal or external water (the remaining 40% were caused by internal or external soil related issues) In addition to presenting this statistical data, the paper also presents opinions and recommendations in several of the above areas particularly those which are felt to be at the core of why so many these structures are exhibiting performance problems. In general, the critical issues appear to be the following; 1. fine grained silt and clay soils used for the reinforced zone backfill, 2. poor placement and compaction of these same fine grained backfill soils, 3. drainage systems and utilities being located within the reinforced soil zone, 4. non-existing water control either behind, beneath or above the reinforced soil zone, and 5. improperly determined and/or assessed design details. Concern over the situation has prompted the creation of an inspector's certification program, i.e., the Geosynthetic Certification Institute's-Inspector Certification Program (GCI-ICP) expressly for MSE walls, berms and slopes using geosynthetic reinforcement.