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A water retention curve (WRC) enables the quick determination of suction in a soil or tailings using the gravimetric water content or degree of saturation. However, establishing the WRC is reliant on time consuming laboratory testing. Here an empirical method is presented that allows the WRC to be estimated quickly, including its void ratio dependency, by relating the fractal and other characteristics of the soil or tailings particle size distributions (PSD) to the parameters which define the WRC. The defining parameters, from a fractal mathematics viewpoint, depend on the particle and pore surface areas and shapes as well as their fractal dimensions. More generally, the clay percentage must also have an important role as it has a major influence on these properties, especially the surface areas. Twelve WRCs for soils and tailings were compiled and compared and used to establish the new empirical expressions. Estimated WRCs using these new empirical expressions compare well with those fitted directly to experimental results. Guidelines are also given on how to quantify suction’s contribution to strength using the location of the hydraulic state on the WRC, adding to the practical appeal of this work.

Internal erosion (suffusion) is caused by water seeping through the matrix of coarse soil and progressively transporting out fine particles. The mechanical strength of soils within water retaining structures may be affected after internal erosion occurs. However, most experimental investigations on the mechanical consequences of internal erosion have used triaxial tests on samples having nonhomogeneous particle size distributions along their lengths. Such nonhomogeneities arise from the most commonly used sample formation procedure, in which seeping water enters one end of a sample and washes fine particles out the other. In this paper a new soil sample formation procedure is presented which results in homogeneous particle size distributions along the direction of seepage, that is at all locations along a sample's length.

An important issue surrounding the identification of liquefaction susceptibility using laboratory testing is how well the soil sample being tested represents the soil in the field. Undisturbed samples are difficult and costly to obtain, while reconstituted soil samples must have a structure and fabric that represents in situ conditions as closely as possible. Recent laboratory tests on sand samples revealed that liquefaction resistance is strongly affected by the sample preparation technique, as different techniques result in different fabrics and structures. The same may be true for silty sand samples, although they have not been given the same research attention. Thus, this paper presents cyclic triaxial test results on non-plastic silty sand samples (a decomposed granite) and determines the number of cycles required to cause liquefaction, considering different failure criterion as well as different confining pressures, cyclic strength ratios and sample preparation techniques. The techniques include dry and slurry deposition. The experimental results show that the preparation technique does not have a significant influence on cyclic resistance.

This paper considers the anisotropy associated with the interparticle contact network and interconnected pore space, which is quantified through a scalar quantity based on the fabric tensor. The study focused on the anisotropy associated with subsets of contacts and pores. It is shown that the stress ratio can be directly related to the geometric anisotropy of strong and non-sliding contacts, and that the anisotropy of pores is correlated with the anisotropy of contacts.

The potential for static liquefaction of tailings is a major focus in the design and operation of tailings storage facilities. This research models the behaviour of unsaturated tailings, with a variety of degrees of saturation, addressing the propensity for static liquefaction during monotonic loading. Unsaturated triaxial tests, including constant suction conditions and constant water–air mass conditions, were performed. A bounding surface plasticity model was used to simulate the results. The constant mass condition is relevant to undrained closed-system loading, which may prevail during fast deformation after the tailings becomes unstable, when the air and water in the pore space remain locked inside the tailings. Boyle's law and hydraulic hysteresis were accounted for to model the changes of pore air and water pressures, and suction, with the change in tailings volume. Good agreement was achieved between test results and model simulations. Additional simulations to mimic rising water tables under constant total stress states in the field, situations that may trigger instabilities, are also shown. Results are added to charts which relate peak and post-liquefaction strengths, as well as collapse lines, to measures of initial state, for unsaturated conditions, which may be of use in practice. [ABSTRACT FROM AUTHOR]

Internal erosion (suffusion) is caused by water seeping through the matrix of coarse soil and progressively transporting out fine particles. The mechanical strength and stress-strain behavior of soils within water-retaining structures may be affected by internal erosion. Some researchers have set out to conduct triaxial erosion tests to study the mechanical consequences of erosion. Prior to conducting a triaxial test they subject a soil sample, which has an initially homogeneous particle-size distribution and density throughout, to erosion by causing water to enter one end of a sample and wash fine particles out the other. The erosion and movement of particles causes heterogeneous particle-size distributions to develop along the sample length. In this paper, a new soil sample formation procedure is presented that results in homogeneous particle-size distributions along the length of an eroded sample. Triaxial tests are conducted on homogeneous samples formed using the new procedure as well as heterogeneous samples created by the more commonly used approach. Results show that samples with homogeneous post-erosion particle-size distributions exhibit slightly higher peak deviator stresses than those that were heterogeneous. The results highlight the importance of ensuring homogeneity of post-erosion particle-size distributions when assessing the mechanical consequences of erosion. Forming samples using the new procedure enables the sample's response to triaxial loading to be interpreted against a measure of its initially homogenous state. Key words: internal erosion, triaxial test, particle-size distribution. L'eau qui s'infiltre a travers la matrice du sol grossier et transporte progressivement les particules fines cause l'erosion interne, appele autrement la suffusion. Le comportement des sols a l'interieur des ouvrages de retenue d'eau en termes de resistance mecanique et de contrainte-deformation peut etre influences par l'erosion interne. Pour etudier les consequences mecaniques de l'erosion, certains chercheurs se sont mis a realiser des essais d'erosion triaxiale. Pour ce faire, ils exposent un echantillon de sol, dont la repartition granulometrique et la densite sont conceptuellement homogenes, a l'erosion en provoquant l'entree de l'eau a une extremite de l'echantillon et en eliminant les particules fines par lavage a l'autre extremite. Pendant cet essai, l'erosion et le mouvement des particules entrainent le deplacement de repartitions granulometriques heterogenes sur la longueur de l'echantillon. Le present article porte sur un nouveau mecanisme de formation des echantillons de sol qui donne lieu a des repartitions granulometriques homogenes sur la longueur d'un echantillon erode. On realise des essais triaxiaux sur des echantillons homogenes formes en utilisant la nouvelle procedure et sur des echantillons heterogenes formes par l'approche la plus utilisee. Selon les resultats obtenus, les echantillons avec des repartitions granulometriques post-erosion homogenes presentent des pics de contraintes de deviation legerement plus eleves que ceux qui etaient heterogenes. Les resultats soulignent qu'il est important d'assurer l'homogeneite des repartitions granulometriques post-erosion pour evaluer les consequences mecaniques de l'erosion. La mise en forme des echantillons en utilisant le nouveau mecanisme permet d'interpreter la reponse de l'echantillon a la charge triaxiale contre une mesure de son etat conceptuellement homogene. [Traduit par la Redaction] Mots-cles : erosion interne, essai triaxial, repartition granulometrique., 1. Introduction Soils may be subject to suffusion, a type of internal erosion, whereby water seeps through the matrix formed by the coarser particles of the soil and progressively removes [...]

Laboratory-controlled cone penetration test results for two silty tailings in a variety of saturated and unsaturated states, obtained using two calibration chambers, are presented then interpreted using a state parameter-based approach. For each, the cone penetration resistances, which increase due to the presence of suction when the tailings are unsaturated, can be normalised using the initial mean effective stress to establish a relationship with the initial state parameter. The relationship is applicable to saturated and unsaturated conditions, as long as the presence of suction hardening as well as the influence of suction on the mean effective stress are accounted for, and as long as the cone penetrations occur under drained conditions. The relationships enable state parameters to be back-calculated from normalised cone penetration resistances. The state parameters enable estimations of the tailings' peak friction angles for drained loadings as well as their propensities to liquefy during undrained loadings. Application is demonstrated using cone penetration test soundings in the tailings storages from which the samples were taken, showing how in situ void ratios and state parameters, as well as future state parameters if the tailings were to become saturated, can be determined. Close agreements with direct measurements of void ratios are shown. [ABSTRACT FROM AUTHOR]

Loess and loess-derived soils in the Akaroa harbour area of New Zealand are typically unsaturated and vulnerable to shallow landsliding during rainfall events. In this paper, the water retention properties and unsaturated shear strength of these materials are characterised using laboratory testing and long-term field instrumentation. Because the pore size distribution of the loess is fractal, the laboratory-derived soil-water characteristic curve is described mathematically using a series of power-law relationships. The same soil-water characteristic curve applies to both recompacted and intact loess when suction is normalised by the air entry value. Stress–strain behaviours of the recompacted and intact loess exhibit significant differences, however. The unique microstructure of the intact loess contributes to its larger shear strength. Long-term field instrumentation data, including suction and volumetric water content, indicate that the hydraulic state of in situ loess remained on a scanning curve for the duration of the monitoring period, despite the occurrence of significant wetting events. This, in combination with triaxial test results, allows the contribution of suction to unsaturated shear strength to be quantified. Temporal variations in suction's contribution to strength confirms seasonal variability in unsaturated shear strength and thus slope stability. [ABSTRACT FROM AUTHOR]

Very little is known about how to interpret cone penetration tests (CPTs) when performed in unsaturated soils. The few published studies on CPTs in unsaturated soils have focused on either clean sands or silt. In this study, new results of laboratory-controlled CPTs in an unsaturated silty sand are presented. Silty sand exhibits hydraulic hysteresis and suction hardening. Suction is observed to have a pronounced effect on measured cone penetration resistance. For an isotropic net confining stress of 60 kPa, it is observed that higher suctions give rise to cone penetration resistances that are 50% larger than those for lower suctions. A semi-theoretical correlation is presented that links measured cone penetration resistances to initial relative density and mean effective stress. Suction has an influence on cone penetration resistances through suction hardening, as well as its contribution to effective stress. For this silty sand, it is shown that failing to account for suction may result in significant overestimations and unsafe predictions of soil properties from measured cone penetration resistances. Key words: unsaturated soil, suction, effective stress, cone penetration test, calibration chamber. On sait tres peu interpreter les resultats d'essais de penetration au cone (EPC) lorsque ceux-ci sont effectues sur des sols non satures. Les quelques etudes publiees ausujet des EPC sur sols non satures se sontinteressees aux sables propres ouaun type de limon. La presente etude porte sur les nouveaux resultats d'EPC controles et effectues en laboratoire sur un sable limoneux non sature. Ce sable limoneux presente une hysteresis hydraulique et un durcissement sous l'effet de la succion. On observe que le phenomene de succion influe beaucoup sur les valeurs mesurees de resistance a la penetration du cone. Dans le cas d'une contrainte isotrope nette de confinement de 60 kPa, on observe que lorsque la succion est elevee, la resistance a la penetration du cone augmente et atteint des valeurs superieures de 50 % a celles enregistrees en presence d'une faible succion. On presente une relation semi-theorique qui relie les valeurs de resistance a la penetration du cone a la densite relative initiale et a la contrainte effective moyenne. La succion influe sur les valeurs de resistance a la penetration du cone par l'intermediaire du mecanisme de durcissement par succion et par sa contribution a la contrainte effective. Dans le cas du sable limoneux etudie ici, on montre que si l'on ne tient pas compte de la succion, on risque d'obtenir des surestimations importantes et des predictions peu fiables des parametres du sol a partir des valeurs mesurees de resistance a la penetration du cone. [Traduit par la Redaction] Mots-cles: sol non sature, succion, contrainte effective, essai de penetration au cone, chambre de calibration., Introduction The cone penetration test (CPT) is widely used for in situ characterization of saturated or dry soils for which interpretation methods are well established (e.g., Robertson and Campanella 1983a, [...]

A calibration chamber has been developed to conduct laboratory-controlled cone penetration tests in unsaturated soils. The chamber allows independent application of lateral and vertical pressures to an unsaturated soil specimen. Horizontal pressure is applied by cell water pressure pushing on a rubber membrane enclosing the specimen, while vertical pressure is maintained by a hydraulic loading ram at the base of the specimen. Suction is controlled using the axis- translation technique. Air pressure is applied to the top of the chamber where it spreads uniformly across the top of the specimen. Pore-water pressure is applied through eight high air-entry value porous disks embedded in the bottom plate. A particularly original aspect of the chamber design is the specimen formation system comprising four moveable cylinder quarters, which enables the creation of specimens of repeatable properties from a variety of soil types. The results of typical cone penetration tests conducted on dry, saturated, and unsaturated sand specimens are presented and highlight the contribution of suction to cone penetration resistance. Key words: unsaturated soil, suction, cone penetration test, calibration chamber, specimen formation, axis-translation technique. Une chambre de calibrage a ete deeveloppeee pour effectuer des essais de penetration au cone controles en laboratoire pour des sols non satures. La chambre permet d'appliquer des pressions laterales et verticales de facjon independantes sur un echantillon de sol non sature. La pression horizontale est appliquee par la pression de l'eau sur la cellule qui pousse sur une membrane en caoutchouc qui entoure l'echantillon, tandis que la pression verticale est maintenue par un belier de chargement hydraulique a la base de l'echantillon. La succion est controleea l'aide de la technique de translation de l'axe. La pression d'air est appliqueiea la partie superieure de la chambre et est distribuee uniformement sur le dessus de l'echantillon. La pression interstitielle est appliquee par huit disques poreux ayant une pression a l'entree d'air eleveie places dans la plaque du bas de la chambre. Un aspect original du design de la chambre est le systeme de formation des echantillons, qui comprend quatre quarts de cylindre mobiles, ce qui assure la creation d'echantillons avec des proprieetes reproductibles pour une variete de types de sols. Les resultats d'essais de penetration au cone typiques realises sur des echantillons de sable sec, sature; et non sature; sont presentes et mettent en evidence la contribution de la succion a la resistance a la peneetration du cone. Mots-cles: sol non sature, succion, essai de peenetration au cone, chambre de calibrage, formation d'eechantillons, technique de translation de l'axe. [Traduit par la Redaction], Introduction The engineering behaviour of unsaturated soils is complex and influenced by many factors including applied stresses, soil type, structure, density, and suction. Most notably, suction increases the soil's strength [...]

The authors of the original paper thank the discusser (Dallo 2020) for his interest in their paper. The expected largest eroded particle size was one of several factors considered in [...]

Summary: Overhangs are frequently observed in riverbanks, coastal headlands, and rock formations. The geometry of an overhang is an input into most slope stability analyses and is often idealised or back‐calculated from empirical data. This study investigates the geometries of overhang slopes, which exist while in limiting conditions satisfying static equilibrium with soil strength governed by the Mohr‐Coulomb failure criterion. The overhanging contour is formulated as the unknown in a boundary value problem and solved for using the slip line theory. Analyses consider nonhomogeneous soils, where cohesion and, if unsaturated, the contribution of suction to the effective stress vary linearly with depth. The solutions are presented in general dimensionless charts. Applications of the charts are illustrated via examples. It has been observed that soil with varying amounts of friction and cohesion could develop overhanging arches of different sizes and shapes. This study shows that the curvature of an overhang becomes more pronounced for small values of φ′. It is also demonstrated that changing the contribution of suction to the effective stress has a direct impact on the size of an unsaturated soil overhang. Overhanging slope shapes observed in reality may be different from the idealised subset studied in this paper since real slopes are not necessarily at impending failure. The real shapes may be influenced by various physical processes such as weathering, stress variations caused by cycles of wetting‐drying. Even so, the results presented in the paper indicated how key soil properties influence slope shapes, albeit it while in limiting conditions. [ABSTRACT FROM AUTHOR]