| Geotechnical investigators use extreme care to saturate lab specimens although most in-situ soils are not saturated. Unsaturated soils contain air as a third phase, which greatly increases the required measurement precision. Controlling the stress state of unsaturated soils involves monitoring the associated stress state variables, (sigma-ua), (ua-u w), and (sigma-uw). The combination of (sigma-u a) and (ua-uw) is most common and these are referred to as the net normal stress and the matric soil suction, respectively.; Matric suction is widely neglected because reliable equipment and methods for testing unsaturated soils are not readily available. Due to the lack of accumulated data, researchers usually choose the cumbersome total stress approach to unsaturated soils problems, which involves matching many soil properties between the lab and field, comparing responses directly without full lab analysis.; This study was intended to help make unsaturated soils testing more common by developing practical, reliable, and robust equipment and methodologies for testing unsaturated soils. The soil testing system developed here can apply suction and total stress; can follow specimen loading and unloading, drying and wetting curves; can measure volume change and water content change, can test 'undisturbed' or remolded specimens; can perform triaxial or hollow cylinder testing; and finally, can produce static or dynamic stresses and strains.; It was not difficult for this testing system to control the stress state of unsaturated soils but it was quite challenging to precisely measure small volume changes. This was overcome by careful design and calibration of the testing system. Detailed methodologies were developed so that a novice could perform complex testing tasks. A new pressure-pulse technique for measuring the volume of diffused air in the system was developed. Finally, recommendations were made for improvements to the system and for future research opportunities.; It is hoped that this study will encourage more engineers to account for matric soil suction and apply this stress state variable to soil mechanics problems. This is a much simpler and more accurate method than the total stress approach, which is often used as a crutch when the necessary physics is not fully understood. |
