The Development of a Suction Control System for a Triaxial Apparatus

摘要

The authors have presented a new suction control system for unsat-urated soils with independent drying and wetting systems and direct measurement of suction. This new technique has several advantages: (1) as stated by the authors "the principal advantage of these systems is that high suction can be controlled without raising the ambient air pressures as is required with the axis-translation technique;" (2) it measures suction directly by means of a high suction tensiometer able to reach 1500 kPa while, for example, techniques based on the relative humidity equilibrium of the system calculate suction indirectly via a thermodynamic relation with the water vapor pressure (e.g., Blatz and Graham 2000; Tang and Cui 2005); (3) the suction range (up to 1500 kPa depending on the tensiometer) provided by this new technique is of most interest for geotechnical engineering problems. This new system can therefore constitute a reliable alternative to the commonly used axis-translation technique. While the technique described by the authors is a major advance in unsaturated soil testing, there are some limitations in what they propose. The discussers are developing a more sophisticated automated system with suction control, building on the work of Cunningham (2000) and Jotisankasa (2005). This more advanced system uses a fully enclosed air circulation system, with computer control of both wetting and drying, and can overcome some of these limitations. Based on the discussers' early experiences and difficulties faced, this note aims to discuss some features of the system as presented by the authors, namely (1) the estimation of water content (and related aspects), (2) suction cycles (reversals), (3) testing duration, and (4) pressure gradients across the sample.