Strength of Weakly Cemented Sands from Drained Multistage Triaxial Tests

Characterizing the strength of weakly cemented and sensitive soils in the laboratory is difficult because of the difficulty in obtaining high-quality replicate samples necessary for defining the failure envelope. Multistage triaxial tests have long been used to reduce the variability caused by testing multiple samples; however, traditional criteria used for transitioning from one loading stage to another often lead to destructuring or failure in sensitive or structured soils. The objective of this paper is to present a methodology for conducting multistage drained triaxial tests on weakly cemented sands and estimating the resulting shear strength parameters. Both multistage and single-stage drained triaxial tests were performed on artificially cemented samples of a silty sand at two levels of densities and cementation. The use of $d{\epsilon }_v/d{\epsilon }_a=0$ as a termination criterion to move on to the next stage of loading and ${\epsilon }_v=0$ as the failure criterion for the final stage of the shear resulted in an average error of 6% and 5% in $c^{\prime }$ and ${\phi }^{\prime }$, respectively, for the stress range considered in this study when compared with parameters obtained from the single-stage drained triaxial tests. Continuous shear wave velocity ($V_s$) measurements during shear showed that destructuring of the cemented samples did not occur by using the proposed termination criterion. The proposed method has the potential to be a cost-effective alternative to the testing of multiple samples for the characterization of the strength of weakly cemented and sensitive soils.