Automated Humidity System for Measuring Total Suction Characteristics of Clay

A computer-automated experimental system for determining total suction characteristic curves using relative humidity control is described. The system is applicable in the relatively high suction range important for fine-grained materials (7000 to 700 000 kPa). The new system has several advantages over existing suction measurement techniques; most notably, it is fully automated, has a much broader measurement range, is capable of determining both wetting and drying characteristics in significantly less time, and requires only one undisturbed sample for testing. Tests are conducted to evaluate the system response and illustrate its use in practice. Total suction characteristic curves are determined for four types of clay, ranging from highly expansive smectite to non-expansive kaolinite. Concurrent characteristic curves are determined using the filter paper method for comparison. Practical applications are demonstrated in two ways. First, select results are analyzed to assess the swelling potential of the four clays using an existing methodology based on total suction testing. Second, aspects related to the adsorption kinetics of expansive soils are evaluated by analyzing the results with a first-order kinetic model.