Effects of freeze–thaw and softening on a natural clay at low stresses

Abstract

Weathering processes such as softening and freeze-thaw cycling affect the properties of clays. Care must therefore be taken when selecting strength and compressibility parameters for analysis of natural slopes, compacted clay embankments, and trench excavations in which significant proportions of the cross section can be affected by climatic weathering.Samples of plastic Lake Agassiz clay from Winnipeg were consolidated anisotropically in the laboratory to axial stresses less than or equal to the in situ effective overburden pressure. They were therefore all overconsolidated with respect to the field preconsolidation pressure. The samples were then loaded under drained or undrained conditions along steeply rising stress paths in p', q stress space. One group of samples was tested immediately to identify the "undisturbed behavior, a second group was subjected to freeze-thaw cycles, and a third group allowed to swell freely before testing.The freeze-thaw cycling produced increased compressibility and pore-water pressures, and reduced strengths at low stresses compared with the behavior of undisturbed clay. Freezing also caused the development of a clearly defined fissure structure. Softening at low stresses with access to water produced less marked effects.Les processus d'altkration tels que le ramollissement et les cycles gel-dCgel affectent les propriCtCs des argiles. 11 faut donc &tre prudent lorsqu'on choisit les paramktres de rCsistance et de comprCssibilitC pour l'analyse des pentes naturelles, des remblais en argile compactCe et des excavations de tranchCes dans lesquels une proportion importante de la section peut &tre affectCe par 1'altCration climatique.Des Cchantillons d'argile plastique du lac Agassiz de Winnipeg ont Ct C consolidCs anisotropiquement au laboratoire sous des contraintes inferieures ou Cgales B la pression effective des terres. 11s Ctaient par consCquent tous surconsolidCs par rapport B leur pression de prCconsolidation. Les Cchantillons ont ensuite Ct C chargCs en condition drainCe ou non-drainCe suivant des cheminements de contraintes montant rapidement dans un espace p', q. Un groupe d'Cchantillons a Ct C test6 immkdiatement pour identifier le comportement "intact," un second groupe a Ct C soumis B des cycles gel-dCgel et un troisikme groupe a Ct C laissi: en gonflement avant essai. Les cycles gel-dCgel ont produit une augmentation de la compressibilitC et des pressions interstitielles et une diminution de la resistance sous faible contrainte, par rapport B 1'Ctat intact. Le gel a aussi produit le dCveloppement d'une structure de fissures clairement dCfinie. Le ramollissement sous faible contrainte avec accks libre de I'eau a produit des effets moins marques.

Softening and instability of natural slopes in highly fissured plastic clay shales

“…soil destructuration caused by cycles of wetting-drying or of freezing-thawing (Botts, 1998;Graham and Au, 1985) and fatigue (Lacerda, 1989;Eigengbrod et al, 1992). Through accumulated plastic strains, all these phenomena, generally concentrated in the most superficial soil layers, can determine a loss of that part of the shear strength that depends on interparticle bonding, causing a reduction in cohesion.…”

Slope stability in slightly fissured claystones and marls

“…Mechanical and chemical reasons explaining the deterioration of shear strength of claystones have been reported by several authors (Terzaghi 1936, Bjerrum 1967, Wilson 1970, Skempton 1970, Morgenstern 1977, Hutchinson 1988. Creeping, suction cycles (highlighted below) and freezing-thawing cycles (of limited intensity in the Iberian Peninsula) also contribute to claystone degradation (Chandler 1972, Tavenas and Leroueil 1981, Graham and Au 1985.…”

Sensitivity Analysis of Factors Affecting Time-Dependent Slope Stability under Freeze-Thaw Cycles

“…In combination with (7), (14), and (17), the relationship of ultimate bearing capacity in micro-rock-unit between the initial state and after N times of freeze-thaw cycles can be obtained as follows:…”

“…K. D. Eigenbrod (1995) and J. Graham (2011) found that the strength, compressibility, and pore water pressure of the fine-grained soil were affected in the case of soil melting [13,14]. Besides, by simulating rock freeze-thaw process, L. Wen et al (2015) studied the changes of mass, volume, uniaxial compressive strength, tensile strength, freeze-thaw coefficient, and weathering degree of saturated hard rock under freeze-thaw cycle effect.…”