Large-scale direct shear testing of geogrid-reinforced aggregate base over weak subgrade

ABSTRACT

Geogrids have been widely used to construct stable subgrade foundations and to provide a working platform for construction over weak and soft soils. Use of geogrid reinforcement in a pavement system ensures a long‐lasting pavement structure by reducing excessive deformation and cracking. In this study, a series of large-scale direct shear tests were performed to evaluate the mechanical interaction between a subgrade soil and an aggregate base layer with and without a geogrid at the interface. The subgrade and base materials consisted of glacial till and well-graded gravel, respectively. Seven types of biaxial geogrids were tested. Normal stresses of 50, 100 and 200 kPa were applied to the top of the samples compacted at optimum moisture content (OMC_soil = 16.4% and OMC_aggregate = 8.2%) to relative compaction values of 93–98% (RC_soil = 94–98% and RC_aggregate = 93–96%). The test results show that aperture area and junction strength of geogrids are important factors that affect the soil–aggregate interface shear strength response. The average values of the peak interface shear strength coefficient, defined as the ratio of the peak interface shear strength of the soil–aggregate systems with and without geogrid at the interface, range from 0.96 to 1.48. Based on the results of this study, the geogrid aperture area, the normalised aperture area, the normalised aperture length, and the junction strength to optimise the peak interface shear strength of soil–aggregate–geogrid systems are 825 mm², 4.7, 5.4, and 11.5 kN/m, respectively. These values are restricted to the materials and test conditions used in this study.

KEYWORDS:

• Large direct shear test
• subgrade
• aggregate base
• geogrid
• interface shear strength coefficient
• aperture size
• junction strength

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgements

This work was supported by the Indiana Department of Transportation through the Joint Transportation Research Program at Purdue University [grant number SPR-3225]. The authors are grateful to the agency for the support. The authors acknowledge the contribution of Min Sang Lee for assisting with the laboratory tests. Thanks are also due to Athar Khan for his valuable comments during the course of this study. The authors thank the reviewers for their constructive feedback and suggestions which helped improve the quality of the manuscript.

Additional information

Funding

This work was supported by the Indiana Department of Transportation through the Joint Transportation Research Program at Purdue University [grant number SPR-3225].