Field Instrumentation and Evaluation of Modular-Block MSE Walls with Secondary Geogrid Layers

Mechanically stabilized earth (MSE) walls reinforced with geosynthetic have been used extensively in highway projects around the world. Typical vertical spacing of geosynthetic reinforcement used in the design of an MSE wall is 0.6 m. This large reinforcement spacing requires a high reinforcement connection strength and may result in wall-facing bulging in the practice. To alleviate such problems, use of secondary reinforcement between primary reinforcement layers was proposed. However, this idea was not verified in the field. In this study, three MSE wall sections reinforced with geogrid layers were constructed and monitored in the field: (1) an MSE wall section with uniaxial geogrid layers as primary and secondary reinforcement; (2) an MSE wall section with uniaxial geogrid layers as primary reinforcement and with biaxial geogrid layers as secondary reinforcement; and (3) an MSE wall section with uniaxial geogrid layers as primary reinforcement only (i.e., the control section). Earth pressure cells, inclinometer casings and probes, and foil-type strain gauges were used in these three test wall sections to measure vertical and lateral earth pressures, accumulated lateral wall-facing deflections, and strains of primary and secondary geogrid layers during construction, respectively. The results from monitoring these three MSE wall sections were analyzed. The test results demonstrated the effects of secondary reinforcement on the improved performance of MSE walls, including reduced accumulated wall-facing deflections, a more uniform lateral earth pressure distribution, and reduced tensile strains in primary geogrid layers.