Differential Settlement of a Geosynthetic Reinforced Soil Abutment: Full-Scale Investigation

About the report:

The Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) uses alternating layers of closely spaced geosynthetic reinforcement and well-compacted granular fill to support the bridge superstructure and form an integrated roadway approach. This system offers simple and rapid construction, lower costs than traditional alternatives, and reduction or elimination of the bump at the end of the bridge. However, like all shallow foundations, GRS-IBS can be vulnerable to differential settlements beneath the foundation.

This report describes research into the behavior of GRS abutments subjected to differential settlements, which may be due to compressible soils beneath the foundation or to scour undermining. A field-scale model was constructed and subjected to carefully controlled differential settlements, and a comprehensive instrumentation program monitored the response of the abutment. The robust response of the abutment under the large differential settlements imposed in these tests indicated that GRS abutments will perform well under the smaller levels of differential settlement that would be expected in field applications. However, if large enough differential settlements occur such that the facing blocks separate, then hydraulic forces could pose a significant hazard to the abutment if the reinforced fill is not adequately protected. Three measures to reduce the vulnerability of the reinforced fill are presented, and a predictive equation was developed to estimate the settlement of the abutment’s facing blocks in response to differential foundation settlement. The predictive equation is specific to the conditions of the field-scale test.

The authors recommend that the Virginia Department of Transportation’s Structure and Bridge Division consider GRS-IBS as a viable bridge technology. For crossings over water, the authors agree with the recommendation of Adams et al. (2011) that GRS-IBS should be considered only if scour concerns can be adequately addressed. In addition, the authors suggest that GRS-IBS designers consider additional measures to protect the reinforced fill in the event of unanticipated settlements.

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