Automated measurement of total suction characteristics in high-suction range - Application to assessment of swelling potential

An automated experimental system to characterize moisture-content-total-suction relationships for unsaturated clayey sons is described. Unlike traditional techniques requiring independent measurement of total suction and moisture content (e.g., thermocouple psychrometry and filter paper), suction is directly controlled and corresponding moisture contents are continuously monitored. The system is applicable for total-suction values ranging between approximately 620 000 and 14 000 kPa. Total suction is controlled during testing by computer-automated rationing of "dry" and "wet" nitrogen gas in a closed environmental chamber. To develop characteristic curves, the equilibrium moisture content of soils placed in the chamber is measured with an integrated electronic balance as water vapor is absorbed or desorbed. The system requires no user intervention and is capable of generating characteristic curves, including wetting and drying loops, in a time span on the order of one to two weeks. Concurrent measurements using the noncontact filter paper method (ASTM D5298) are shown to agree very closely with those obtained from the automated system. Total-suction characteristic curves are compared for a highly expansive smectite clay and nonexpansive kaolinite clay. Hysteresis between the wetting and drying cycles and stepwise dehydration phenomena, which have been noted by previous researchers, are reproduced in the results. Comparison of the smectite and kaolinite characteristic curves demonstrates the system's potential to become a simple, non-labor-intensive, quick, and reliable platform to qualitatively assess the relative swelling potential of clayey soils.