Observations from load tests on geosynthetic reinforced soil

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2014-05

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University of Hawaii at Manoa

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In lieu of conventional concrete cantilever retaining walls, geosynthetic reinforced soil (GRS) is increasingly being used as bridge abutments to support single span bridges. When backfilled with cohesionless material, GRS abutments have good drainage, large bearing capacities, and great flexibility to withstand seismic loads and do not suffer from the bump-at-the-end-of-the-bridge syndrome. GRS differs from geosynthetic mechanically stabilized earth (GMSE) structures in many ways particularly with respect to reinforcement spacing. The reinforcement spacing in GRS is closer (typically 8 inches) whereas the spacing in GMSE can be as large as 32 inches. Four pairs of instrumented GRS square columns, also known as performance tests or mini-piers, were load tested at the Turner-Fairbank Highway Research Center (TFHRC) in McLean, Virginia from 2011--2012. Each pair consisted of identical reinforcement strength to spacing ratio, backfill, and dimensions; however, one was loaded with a light-weight dry-stacked friction-only concrete masonry unit (CMU) facing in place and the other with the CMU removed prior to load testing. Moreover, each pair had different reinforcement strength (Tf) and vertical spacing (Sv). The effects of the CMU facing and varying Tf, Sv and Tf/Sv ratios on the GRS vertical capacity, load-settlement curves, lateral deformation and lateral earth pressures during mini-pier construction and during load testing were investigated. A method to deduce the composite shear strength parameters using stress paths for pairs of these mini-piers was developed; the validity of the postulate of zero volume change was investigated; and the appropriateness of using fully softened versus peak backfill shear strength parameters to predict the bearing capacity of a footing on a GRS abutment was studied.

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GRS, bridges, reinforcement spacing

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Theses for the degree of Master of Science (University of Hawaii at Manoa). Civil Engineering.

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