Synopsis Artificially sedimented specimens of Wyoming bentonite (Volclay) were used to investigate the effect of physico-chemical variables on the consolidation properties of montmorillonite. One-dimensional consolidation tests were performed on calcium and sodium montmorillonite at various electrolyte concentrations. The influence of pH and organic pore fluids on the consolidation properties of montmorillonite was also investigated. The consolidation curves of calcium montmorillonite were essentially independent of both the electrolyte concentration in the free pore water and the pH of the suspension from which the specimens were sedimented. The influence of pore water electrolyte concentration on the swelling curves of calcium montmorillonite was much smaller than would be predicted from the Gouy-Chapman double layer theory. The consolidation and swelling curves of sodium montmorillonite were affected by the concentration of electrolyte in free pore water and there was reasonable agreement between the measured swelling curves and the double layer theory. Consolidation tests in which organic pore fluids were used demonstrated that swelling of montmorillonite is caused by either adsorption of the pore fluid or formation of diffuse double layers. The coefficient of permeability of the sodium montmorillonite in water was as low as 2 × 10−l2 cm/s. The coefficients of permeability were higher for the montmorillonite in ethanol than in water, and considerably higher values were obtained when the pore fluid was non-polar, all compared at the same void ratio. On a utilisé des échantillons artificiellement sédimentés de bentonite du Wyoming (Volclay) pour étudier l'effet des variables physico-chimiques sur les propriétés de consolidation de la montmorillonite. On a fait des essais de consolidation unidimensionnelle sur les formes calcium et sodium de la montmorillonite à diverses concentrations d'électrolyte. On a également étudié l'influence du pH et des liquides de pore organiques sur les propriétés de consolidation de la montmorillonite. Les courbes de consolidation de la forme calcium de la montmorillonite sont essentiellement indépendantes de la concentration d'électrolyte dans l'eau libre des pores et du pH de la suspension à partir de laquelle on a fait sédimenter les échantillons. L'influence de la concentration en électrolyte dans l'eau des pores sur les courbes de gonflement de la forme calcium de la montmorillonite est beaucoup plus faible que ne permet de le prévoir la théorie de la double couche de Gouy–Chapman. Les courbes de consolidation et de gonflement de la forme sodium de la montmorillonite sont influencées par la concentration en électrolyte dans l'eau libre des pores et il y a un assez bon accord entre les courbes de gonflement mesurées et la théorie de la double couche. Des essais de consolidation effectués en utilisant des liquides de pore organiques ont démontré que le gonflement de la montmorillonite est dû soit à l'adsorption du liquide de pore, soit à la formation de doubles couches diffuses. Le coefficient de perméabilité de la forme sodium de la montmorillonite est aussi bas que 2 × 10−12 cm/s. Les coefficients de perméabilité sont plus élevés pour le systéme montmorillonite éthanol que pour le système montmorillonite eau, et on a obtenu des valeurs considérablement plus élevées lorsque le liquide de pore était non-polaire, toutes ces mesures étant ramenkes à la même fraction de vide.

The purpose of this paper is to review the state of the art in the measurement of hydraulic conductivity of fine-grained soils. Both field and laboratory tests for saturated and partially saturated soils are considered. For saturated soils, field tests are to be preferred because they permeate a larger volume of soil, thus taking into account the effects of macrostructure better than laboratory tests. Field tests are generally best performed by using a cylindrical piezometer tip, installed by methods that minimize disturbance, and measuring flow under a constant head. Laboratory tests offer the advantage of economy. Laboratory specimens should be as large as practical and should be oriented to produce flow in the direction of maximum hydraulic conductivity. The permeant should be a fluid similar to that encountered in the field. Without proper experimental technique, the conductivity measured in the laboratory may differ from the field value by several orders of magnitude. Field tests for unsaturated soils are not well developed and can only be recommended for cases where water will be ponded on the surface of a site. The most versatile laboratory techniques are the instantaneous profile method using tensiometric or psychrometric probes, and the pressure plate outflow method. The best method to use depends on the soil suction expected in the field.

Compacted soil liners have been used to retard leakage of fluids from burial sites. If allowed to desiccate, such liners may shrink, crack, and lose their integrity. As a result of the expense and control problems associated with field tests, an initial laboratory study was made of shrinkage, cracking tendency, and hydraulic conductivity of various compacted clay/sand mixtures. The study showed that desiccation shrinkage increased linearly with compaction water content and was unaffected by density. Soaking prior to desiccation increased strains markedly for specimens compacted dry of optimum. Shrinkage strains greater than 10% should cause serious problems in the field. Clay/sand mixtures were prepared which were crack resistant and which had low hydraulic conductivities.

The state of the art of consolidation testing is addressed except that conditions involving generalized stress states were excluded and large-strain problems were assigned to a companion paper. Terzaghi's classical theory was found to fit primary data rather well and the root time fitting method was preferred. Errors associated with boundary impedance and ring friction can be major but are generally understood and can be minimized. Existence of nonlinear stress-strain relationships can perturb the shape of S-t curves significantly and lead to problems when pore pressures are used to determine cv. Radial flow tests should be used for field problems involving horizontal flow; theories are presented to use in reducing laboratory data. Secondary effects can be addressed using linear theory and trial solutions, but such effects may be much more apparent in the laboratory than in the field. Effects of partial saturation are understood qualitatively and can influence laboratory data greatly. Continuous loading tests lead to overprediction of effective stresses but apparently to reasonable values of cv. Soil properties change significantly as a result of sampling disturbance and storage time; techniques for correcting for these effects are presented. The usefulness of laboratory data is examined using a case history.

Increased interest in protection of the environment has led to a need to be able to predict long-term movement of moisture, and contaminants, in the vicinity of shallow land disposal sites for various toxic and radioactive wastes. The advantages of locating potential sites in arid regions has led to a need to develop means for predicting moisture movements in fairly dry, partially saturated soils and for measurements of the hydraulic conductivities of such soils. A technique was developed in which thermocouple psychrometers and the instantaneous profile method were used to measure conductivities of soils with suctions as high as 80 atm. For one clay of low plasticity, the conductivity dropped from about 10−7 cm/s when saturated to almost 10−12 cm/s for degrees of saturation of the order of 30 percent. Measured conductivities were used in a finite element solution to Darcy's equation to predict final water content profiles. The predicted and measured profiles compared well, which suggests that the measured conductivities were tolerably accurate. Based on data presented, the proposed technique seems promising for conductivity measurements in clays with degrees of saturation between about 30 and 90 percent and in sands with 5 to 50 percent saturation.