An Evaluation of Three Triaxial Systems With Results From 0.1 to 100 MPa

Abstract

Abstract This paper evaluates the results of triaxial tests carried out over a very wide range of effective stresses using custom-built triaxial systems specially developed for testing at low, medium, and high pressures. These tests were performed on samples of resedimented Boston Blue Clay, and good reproducibility is demonstrated across testing devices. A novel approach was taken to evaluate the effect of apparatus compressibility of the drainage system on the measured undrained shear behavior, as this issue becomes increasingly important for triaxial testing at high stresses. The effect of apparatus compressibility on triaxial shear results was evaluated by comparing the volume of pore fluid necessary to develop the drained strength of a specimen to the volume of flow caused by apparatus compressibility. This method is more illustrative and intuitive for undrained triaxial testing of saturated specimens than the traditional approach of using a specimen's B-value. Triaxial test results show a consistent decrease in both undrained strength ratio and critical state friction angle over the effective stress range of 0.1 to 100 MPa for each overconsolidation ratio investigated. The conventional assumption made in soil models that fine-grained soils exhibit constant normalized strength properties is therefore shown to be invalid when these properties are viewed over a significant range of effective stresses.