Resumen

A mechanically stabilized earth (MSE) wall and berm is being constructed as part of the expansion of Cherry Island Landfill in Wilmington, Delaware. Because the berm is being constructed over weak, compressible foundation soil comprised of reclaimed dredge material, high strength geotextile was incorporated into the design as base reinforcement to improve global stability. Even with the inclusion of this reinforcement, large magnitude vertical and horizontal displacements are anticipated, and the potential for deep-seated failure exists. Consequently, an extensive instrumentation program comprised of inclinometers, piezometers, and settlement devices was designed to observe wall movements and pore pressure increases in the soft foundation soils over time. An additional monitoring system was employed at four of the more critical wall sections, by attaching strain gages to the high strength geotextile to ensure that stresses in the geotextile did not become too large during staged construction. Prior to installation, calibration testing of geotextile specimens established relationships between electrical resistance in the gages, tensile strain, and tensile force for subsequent in-situ monitoring. Regular monitoring of the installed strain gages provided direct feedback of geotextile performance by indicating the degree of stress development under field load.

Two years into the project, construction of the MSE wall and berm is approximately 60% complete. Significant vertical and horizontal displacements have been observed, as much eight and three feet, respectively. Typical observed tensile strain in the geotextile ranges between 0% and 2%, significantly lower than the design strain of 6.6% and in good agreement with similar reinforcement monitoring projects. Field data from the instrumentation program is presented and discussed, and global stability of the MSE wall and berm is analyzed.