Mechanically Stabilized Earth (MSE) retaining walls on transportation projects are generally conservatively designed, using "low fines" reinforced soils. Four full-scale field tests were conducted, in order to establish properties for "high fines" reinforced soils and associated design controls that give acceptable MSE wall performance. The walls were constructed with wire basket face elements and polyester geogrid reinforcement, except that one wall used geotextile reinforcement. The field tests included provisions to demonstrate the role of pore water pressure in the reinforced fill and the importance of including a positive drainage system to obtaining good wall performance. The full-scale field test program is funded by the Transportation Research Board, under National Cooperative Highway Research Project (NCHRP) HR 24-22. The objective of the Project is to develop selection guidelines, soil parameters, testing methods, and construction specifications that will allow the use of a wider range of reinforced fill materials within the reinforced zone of mechanically stabilized earth (MSE) walls. The estimated potential savings from replacing AASHTO reinforced fill materials with "higher fines" reinforced fill materials could be in the range of 20 to 30% of current MSE wall costs. This paper presents some of the results of the field tests on four full-scale test walls and documents the basis for our conclusions that MSE retaining walls on transportation projects using backfills with fines up to 25% with a plasticity index less than 6% will deliver acceptable performance provided positive drainage measures are included at the back of the reinforcement and provisions are made to prevent surface water from entering the backfill.
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