Discussion of “From saturated to unsaturated conditions and vice versa” by Martí Lloret-Cabot,Simon J. Wheeler,Jubert A. Pineda,Enrique Romero,and Daichao Sheng (https://doi.org/10.1007/s11440-017-0577-6)

The authors (Lloret-Cabot et al. in Acta Geotech 1–23, 2017) applied the glasgow coupled model (GCM), originally proposed by Wheeler et al. (Géotechnique 53(1):41–54, 2003), to the simulation of several experimental tests that involve transition between saturated and unsaturated states. The authors show qualitatively, but not quantitatively, predictions of GCM for shrinkage during air drying of normally consolidated samples (Fig. 13) under low mechanical stress conditions, without presenting the material parameters. The discussers, who have worked with GCM to model multilayer deposition of tailings/soft soils (Qi in Numerical investigation for slope stability of expansive soils and large strain consolidation of soft soils. Doctoral dissertation, University of Ottawa, 2017; Qi et al. in J Geotech Geoenviron Eng 143(7):04017018, 2017, Qi et al. J Geotech Geoenviron Eng 143(7):04017019, 2017), have made quantitative predictions of similar cases. Satisfactory simulations of such cases using GCM are sensitive to the selection of the coupling parameters k₁ and k₂. By considering an alternative analytical form of GCM, an analytical procedure can be derived for calibrating the coupling parameters for problems involving virgin drying.     

Axis Translation and Negative Water Column Techniques for Suction Control

Negative water column and axis translation techniques are conventionally used experimental techniques for obtaining data to interpret the engineering behavior of unsaturated soils. The negative or the hanging water column technique is used as a suction control method in the low suction range (i.e., 0–30 kPa). The axis translation technique is used in the suction range 0 to 500 kPa or higher. This technique is particularly useful for testing specimens with suction values greater than 100 kPa avoiding problems associated with cavitation. While the axis-translation technique has been commonly used, the limitations associated with this technique related to air diffusion, water volume change and evaporation are not discussed in greater detail in the literature. This paper highlights some of the key aspects related to the negative water column and axis translation technique that are of interest both to the researchers and practicing engineers.     

Influence of rain infiltration on the stability of compacted soil slopes

Stability analyses for a homogeneous compacted embankment were undertaken considering infiltration of water into the embankment. The analyses include several different practical scenarios: (i) saturated condition, (ii) ponding (or runoff) along with saturated condition, (iii) short term analysis for unsaturated conditions, and (iv) long term analysis for unsaturated conditions. The appropriate shear strength parameters of the compacted soil required for analyzing different practical scenarios were determined using conventional and modified triaxial shear apparatus. The results of the study show that typically shallow circular failures above water front occur due to infiltration rather than the conventional infinite slope type failures.     

Stress-path dependent behavior of a weathered clay crust

Triaxial compression and oedometer consolidation tests are commonly performed to evaluate the strength and deformation behavior of soils. However, in the field, the stress paths imposed by various engineering works may deviate from the stress paths conventionally used in laboratory tests. Moreover, the stress-paths followed by different soil elements under a foundation are different. To obtain representative soil parameters, the laboratory stress path should be similar to that followed in the field. In this study, a significant number of stress-path triaxial tests, with stress probes in various directions, have been conducted to study the stress-path dependent behavior of an overconsolidated weathered crust of Champlain clay in Eastern Ontario. Both undrained and drained tests have been conducted for samples isotropically consolidated to the in situ vertical stress and anisotropically consolidated to in situ state of stress. The yield locus of the clay crust has been defined. It has been observed that the strength-deformation and yielding behavior of this weathered clay crust highly depends on the stress-path as well as on the in situ stress history.     

Modelling virgin compression line of compacted unsaturated soils

Acta Geotechnica - In this paper, the volumetric collapse of an unsaturated soil, upon soaking to saturation under a certain stress level, is referred to as soaking collapse. The soaking collapse...     

Change in pore-size distribution of collapsible loess due to loading and inundating

Acta Geotechnica - It is well known that the hydromechanical behavior of both saturated and unsaturated loess soils is significantly influenced by the soil fabric. However, there is limited...     

Water percolation in a thick unsaturated loess layer considering the ground‐atmosphere interaction

The key objective of this paper is to advance our present understanding of how surface water infiltrates in thick unsaturated loess, which is found in arid and semiarid regions of the world, considering the ground‐atmosphere interaction. In situ data for a period of 1 year in thick loess layer at a site in the Loess Plateau of China that has groundwater table at 97.5 m depth were collected for achieving this objective. Climate factors, mainly rainfall and actual evaporation, were measured. In addition, variations of soil temperature and water content at different depths in the unsaturated zone were also measured. The data were used to interpret the water percolation characteristics by dividing the thick unsaturated zone into three zones; namely, (i) surface zone, which constitutes the top 1.0 m, (ii) unsteady zone, which is from 1.0 to 7.0 m, and (iii) steady zone, which is below 7.0 m. In the surface zone, soil temperature and water content are sensitive to climate factors. There is a variation of water content associated with the cumulative influence of infiltration and evaporation in the precipitation and nonprecipitation periods, respectively. In the unsteady zone, the water content is relatively constant; however, temperature varies in different seasons. Water percolation in this zone is both in liquid and vapour phases. In the steady zone, both soil temperature and water content are constant during the entire investigation period. The percolation velocity in this zone is approximately 1.23 × 10^?8 m/s or 0.39 m/year, which suggests that it will take approximately 230.8 years for surface water to pass through the thick unsaturated zone and recharge the groundwater.     

Soil freezing process and different expressions for the soil-freezing characteristic curve

The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions (i.e., power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils (i.e., sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper.