Optimization of Advanced Laboratory Monotonic and Cyclic Triaxial Testing on Fine Sands

Monotonic and cyclic triaxial testing provides key information for a wide range of sensitive geotechnical problems. This paper assesses the potential impact on stress-strain measurements of several error sources and discusses how test quality may be improved. External volume-gauges are shown to be subject to significant errors that depend on pressure level. While high-resolution local radial strain measurement presents considerable challenges, especially in long duration cyclic tests, problems with ‘floating’ radial-belts and alternative ‘L-configuration’ systems were overcome by steps that allow strains as low as 10-4 % to be resolved reliably. Sample end conditions are shown more important than is commonly appreciated. Employing smooth enlarged and lubricated end platens can avoid the recording of misleadingly high shear resistances, which are most significant with relatively loose specimens tested under low effective stresses. Stiffnesses and dilation trends were also recorded more reliably in tests employing smooth enlarged and lubricated end platens. The arrangements overcome significant strain errors even in tests employing local instruments and specimens with initial height-to-diameter ratios of two.