Characterization of Compacted Silty Sand Using a Double-Walled Triaxial Cell With Fully Automated Relative-Humidity Control

Abstract

A fully automated relative-humidity (auto-RH) control unit has been adapted to a newly implemented double-walled triaxial cell to test unsaturated soils under higher total suction states via the vapor-pressure technique, allowing for direct measurement and control of the relative humidity inside the pores of the test soil. The triaxial system is also suitable for implementing the axis-translation technique. With the operational and fully integrated servo-controlled triaxial system, a series of conventional triaxial compression (CTC) tests were conducted on identically prepared specimens of compacted silty sand under constant total suction states of 20 MPa and 300 MPa, induced and controlled via the automated auto-RH control unit. The suitability and reliability of the integrated system was demonstrated by closely repeatable results obtained from the series of suction-controlled CTC tests. Suitable shearing rates for suction-controlled testing of compacted silty sand, via both axis-translation and relative-humidity-based techniques, were also empirically assessed through a series of strain-/suction-controlled tests. The latter were conducted at different axial loading rates (% axial strain per unit time) under either constant matric suction (0.5 MPa) or constant total suction (300 MPa). In both cases, the most suitable shearing rate was identified as the maximum rate for which the test soil continued to be subjected to a constant matric or total suction throughout the entire shearing stage.