Isotropic compression and triaxial shear behaviors of cement- and cement-gravel-treated granite residual soil for use as subgrade filling

The easy-disintegration nature and weak mechanical properties of granite residual soil (GRS) hinder its utili-zation as subgrade and embankment fillings. In this study, cement additive was used to introduce artificial interparticle cementation, and gravel additive was used to introduce coarse skeleton. Isotropic compression and triaxial shear tests were conducted on saturated cement-treated and cement-gravel-treated GRS to determine their compressibility and drained strength. Results show that, for the saturated cement-treated GRS, the post -yielding compression parameter (lambda post-yielding) involved non-monotonic with the volumetric cement content (Cvi) and peaked at Cvi = 3%; its effective strength parameters (c' and phi') peaked at Cvi = 2 -3%. Adding gravel markedly decreased the compressibility and increased the drained strength of the cemented GRS. For the saturated cement-gravel-treated GRS, the pre-yielding compression parameter (lambda pre-yielding) involved non -monotonic with the volumetric gravel content (CvG) and troughed at CvG = 20 -30%; its c' and phi' peaked and troughed at CvG = 20 -30%, respectively. These non-monotonic correlations may be because macro -porosity of the cured specimens reached the lowest at Cvi = 2 -3% and a global gravel skeleton formed at CvG = 20 -30%. Hence, a cement dosage of Cvi = 2 -3% is suggested for treating the GRS (a silty sand) before it can be used as subgrade filling, and cement-gravel treatment with CvG = 20 -30% can be further considered to minimize the cement dosage and obtain higher geotechnical performance of the treated soil.