To investigate the effect of graphene (G) on the triaxial mechanical characteristics of cement stabilized soil, a triaxial unconsolidated and undrained (UU) test was conducted on cement stabilized expansive soil (CES) and graphene-modified cement stabilized expansive soil (GCES) with 0.05%, 0.1%, 0.15%, and 0.2%G content, respectively. The experimental results showed that compared with CES, the deviatoric stress-strain curve of GCES showed a more obvious softening characteristic. The addition of G had a good modification effect on the triaxial mechanical characteristics of CES, and with the increase of the content of G, the compressive strength and shear strength of CES increased first and then decreased, and reached the best value when the G content was 0.1%. The failure angle predicted by the Mohr-Coulomb failure angle formula had a good correlation with the measured failure angle of soil specimens, so it could provide help for the prediction of soil failure surface in practical engineering. Besides, the scanning electron microscope (SEM) analysis indicated that the internal structure of CES was improved due to G addition.

To improve the limitations of lime-treated subgrade soil (LS), a series of unconsolidated and undrained triaxial tests were conducted to investigate the improvement effect of fiber modified lime-treated soil (PLS) and fly ash modified lime-treated soil (FLS). The test results showed that (1) The deviatoric stress-strain curves of LS, PLS, and FLS were basically of the softening type. (2) The addition of fiber and fly ash improved the ductility and stiffness of LS. The ductility of PLS increased by 134% compared with LS, while the mechanical strength of FLS increased by 53%. (3) The microscopic tests showed that a denser skeleton structure was generated inside LS with the addition of fiber and fly ash. (4) The deviatoric stress-strain curves of LS, PLS, and FLS under different confining pressures were better characterized with the CES curve model. The above results indicate that fiber and fly ash can effectively improve the mechanical characteristics of lime-treated subgrade soil.