Effects of Specimen Saturation on Strength Reduction in Triaxial Tests: Monotonic and Cyclic Case Studies

Degree of saturation of soil is an important factor in preparing specimens of soil in the laboratory. The moisture content of the specimen affects its behavior, especially in undrained loading, either by change of the structure of soil or by change of effective stress path. Even though special equipment is required to measure the change of unsaturated specimen’s geometry, they are not provided in many engineering laboratories due to economic and technical reasons. One alternative for a precise measurement is to saturate the specimens. We show herein that apart from such expensive measurements and saturating the specimens even though it is not saturated in the field, estimating the change of specimen size by simplifying the relevant assumptions and resembling the degree of saturation of the field in the laboratory is to be preferred. Two case studies of monotonic and cyclic triaxial tests are reported herein to show this priority based on field tests and image processing results. It is concluded that given the variation of the degree of saturation of the soil in the field, as well as its volumetric behavior while being sheared, that is, either being compressional or dilative, are essential to make the optimal decision on the selection of the proper degree of saturation at the laboratory.