Effect of Cementation on the Shear Strength of Tehran Gravelly Sand Using Triaxial Tests

Coarse-grained soils of Tehran are cemented. These soils are heterogeneous not only in gradation and density but also in cementation. Due to this heterogeneity and the extreme difficulty in obtaining undisturbed samples, artificially cemented specimens using lime as the cementing agent are used to understand the effects of cementation on the shear strength parameters. A base soil with 45% gravel, 49% sand and 6% fine material was used, based on gradation curves of the coarse-grained soils of Tehran. Specimens were prepared by mixing the soil with 1.5, 3, and 4.5 percent lime and after curing were tested using triaxial compression tests. Specimens were also tested in uncemented and destructured conditions. The results of the tests indicated that the cementation increases peak shear strength, suggesting an increase in cohesion. Cemented specimens show a brittle failure mode at low confining pressure with a transition to ductile failure mode at higher confining pressures. The stress-strain curves for cemented specimens show a clear peak stress followed by a sudden drop in stress and strain softening. There is no clear peak in shear stress for uncemented and destructured specimens. The failure envelope is curved for cemented specimens. The influence of cementation on the friction angle of the tested specimens is a function of confining pressure, and degree of cementing. The results show that the peak friction angle at low confining pressure increases with increasing cementation.