The Axis-Translation and Osmotic Techniques in Shear Testing of Unsaturated Soils: A Comparison

Abstract

Matric suction in the laboratory testing of an unsaturated specimen is usually controlled by the axis-translation technique or the osmotic technique. To investigate possible diŠerences in the axis-translation and osmotic techniques in shear testing of unsaturated soils, three series of unsaturated triaxial shear tests were conducted on a compacted expansive clay with an initial degree of saturation of 82z. Two of these series were performed using the axis-translation and osmotic techniques at HKUST. Another series was performed using the osmotic technique at ENPC. In the series using the axis-translation technique, the single-stage testing procedure was compared with the multi-stage testing procedure and these two testing methods were found to provide consistent shear strength information. The consistency of the results from the osmotic technique at HKUST and ENPC demonstrated the reliability of the osmotic technique. Based on the extended Mohr-Coulomb shear strength formulation, comparison of the results using the axis-translation technique and the osmotic technique showed that there was no diŠerence in determining the internal friction angle, q?. However, the values of q b in the test series using the axis-translation technique were slightly larger than those in the test series using the osmotic technique by 39 -49 .

Review of fundamental principles in modelling unsaturated soil behaviour

“…[80,6]). In this case, the air pressure is used as a reference value for stress measures and the net stress is the total stress in excess of the pore air pressure.…”

Comparisons of Different Suction Control Techniques by Water Retention Curves: Theoretical and Experimental Studies

“…Figure 4 shows the relationship between the concentration of the PEG solution and the osmotic pressure. In this study, the calibration was carried out using an osmotic pressure cell introduced by Ng et al (2007) under a room temperature of 25 ± 1°C. PEG 20000 (molecular weight value = 20,000) and a Spectrum 14000 semipermeable membrane (molecular weight cut‐off value = 14,000) were used.…”

“…At PEG solution concentrations <20%, the calibration curves obtained using the three methods are consistent. At higher PEG solution concentrations, however, the curves are noticeably different, probably due to the membrane effect (Dineen and Burland, 1995; Ng et al, 2007; Delage and Cui, 2008). In the calibration using an osmotic pressure cell and an IC suction probe, equilibrium was achieved through water flow.…”

“…Total suction is generally recognized to have two components: matric suction and osmotic suction (Aitchison, 1965). Various suction control techniques have been developed including the axis‐translation technique (ATT) (Hilf, 1956) and the osmotic technique (OMT) (Zur, 1966) to control matric suction and the vapor equilibrium technique (VET) (Tessier, 1984) to control total suction (Agus and Schanz, 2005; Ng et al, 2007; Tarantino et al, 2011; Laloui, 2013).…”

Performance of high-capacity tensiometer in constant water content oedometer test

“…The axis-translation technique hinders cavitation in the unsaturated soil specimen which is unnatural as the air pressure in the field condition is not artificially elevated [4] and can only be justified if the water is rigid [13]. The effect of cavitation on the unsaturated soil specimen is unclear but some experimental tests using osmotic suction gave different results compared to tests using the axis-translation technique [17,25,26].…”