Development of a multifunctional triaxial system for unsaturated soils: Addition of permeameter function

The details of a multifunctional triaxial system developed for unsaturated soils over the past ten years at The University of Tokyo are described. This study first briefly reviewed three functions of the triaxial system developed for the undrained cyclic loading test to evaluate liquefaction properties of unsaturated soils. In the triaxial system, accurate measurement of volumetric deformation was achieved with a linkage double cell system, application of the membrane filter technique gave prompt measurements of matric suction, and a p-constant control system well maintained a constant condition of total mean principal stress p. The article later described a newly developed permeameter function of which delicately designed local pin sensors (LPSs) and inflow/outflow measurement devices were introduced to the triaxial system for measurement of coefficient of permeability of unsaturated sandy specimens. The permeameter maintained constant water levels at inflow and outflow ends, and the flow rates were monitored by sensors. LPSs, as local sensors to directly measure water head difference, were manufactured with the membrane filter technique, a technique to measure or control suction. Typical permeability test results on saturated and unsaturated specimens were presented. For unsaturated specimens, constant hydraulic heads were supplied, and the same inflow and outflow rates were achieved. Meanwhile, local pore water pressures measured by LPSs well reflected specimen conditions. It was verified from this and past studies that the permeameter system can be applied to unsaturated specimens with coefficient of permeability in a range of 10^-5to 10^-8m/s.