The development of a suction control system for a triaxial apparatus

A new method of controlling suction in the triaxial apparatus is presented that consists of two subsystems: one each for drying and wetting that is used in combination with an independent measurement of suction. The drying system is based on a development by Cunningham et al (2003), with improvements in the measurement of the current water content. The wetting system involves the staged circulation of air and water. This new technique enables continuous monitoring of all state variables during tests, including water content, degree of saturation, net stresses, suction, and the different components of strain. Some typical results from tests on a compacted silty clay are presented in order to demonstrate the capabilities of the system. The main advantage of the apparatus is that there is no need to raise the ambient air pressure as is required with the axis translation technique and tests may therefore be conducted at negative pore water pressure. The system may also be easily incorporated into other standard apparatus.