Investigation of geogrid-reinforced unbound granular material behavior using constant radial stiffness triaxial tests

Abstract

A series of constant radial stiffness triaxial (CRST) tests were performed to investigate the long-term behavior of geogrid-reinforced unbound granular materials (UGMs). Two types of multi-stage cyclic loading tests were conducted with various vertical constant loads (${\sigma }_{1,\min }$). In the first type, ${\sigma }_{1,\min }$ was maintained at 10% of the maximum axial stress at each loading stage to determine the resilient modulus. The results indicated that the inclusion of geogrid increased the resilient modulus by 21–25 MPa under various cyclic loads. In the second type of tests, three tests were performed with ${\sigma }_{1,\min }$ of 5, 10, and 20 kPa, respectively, to investigate the effects of vertical constant loads on the contributions of geogrids to the confining stress and permanent deformation. The results showed that the inclusion of geogrid mitigated permanent deformation by enhancing the confining stress. However, an adverse effect of the geogrid on permanent deformation was observed when ${\sigma }_{1,\min }$ was 5 kPa, which can be attributed to the loss of contact between the geogrid and aggregates. Furthermore, R-values and stress paths obtained in this study also demonstrated the capability of CRST tests in quantifying the effects of geogrids on UGMs under cyclic loadings.