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This paper presents an investigation of the microstructure and cementation of two carbonatic fine-grained soils obtained from a deposit of lacustrine origin formed during the Wisconsin glaciation. The two soils differ in the degree of cementation (with average total carbonate contents of ~55% and ~38%), the dominating carbonate mineral (calcite versus dolomite), and the forms of carbonates present. The study is founded on observations of the microstructure using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray (EDX) spectrometry, and examination of the effects of carbonate dissolution on Atterberg limits and particle-size distribution. In both soils, the majority of the carbonate is in the form of a coating layer on the clay and silt particles, with a thickness less than 2-3 p.m, and decreasing in the sample with lower carbonate content. This coating layer 'networks' particles and groups of particles. Carbonate cementation impacts the engineering properties of both soils, and the site's overconsolidation ratio (OCR) profile clearly reflects changes in carbonate content and microstructure. One-dimensional compression tests show that cementation is associated with a moderate degree of structuring, and that the resulting structure is stable, with no complete destructuration occurring even after the effective stress exceeds 10 times the preconsolidation stress. Key words: calcite, dolomite, mineralogy, cementation, soil structure, scanning electron microscopy, energy-dispersive X-ray. Cet article presente une etude de la microstructure et de la cimentation de deux sols a grains fins carbonates obtenus a partir d'un gisement d'origine lacustre forme pendant la glaciation du Wisconsin. Les deux sols different a la fois par le degre de cimentation (avec des teneurs moyennes en carbonate total de ~55% et ~38%), le carbonate dominant (calcite versus dolomite) et les formes de carbonates presents. L'etude est fondee sur des observations de la microstructure a l'aide de la microscopie electronique a balayage (MEB) equipee d'une spectrometrie a rayons X a dispersion d'energie (EDX); et l'examen des effets de la dissolution du carbonate sur les limites d'Atterberg et la distribution granulometrique. Dans les deux sols, la majorite du carbonate se presente sous la forme d'une couche de revetement sur les particules d'argile et de limon, d'epaisseur inferieure a 2-3 p.m, et decroit dans l'echantillon avec une teneur en carbonate plus faible. Cette couche de revetement<< met en reseau >> des particules et des groupes de particules. La cimentation des carbonates a un impact sur les proprietes mecaniques des deux sols, et le profil du ratio de surconsolidation (<< OCR>>) du site reflete clairement les changements dans la teneur en carbonate et la microstructure. Les essais de compression unidimensionnelle montrent que la cimentation est associee a un degre modere de structuration et que la structure resultante est stable, sans destructuration complete meme apres que la contrainte effective depasse 10 fois la contrainte de preconsolidation. [Traduit par la Redaction] Mots-cles : calcite, dolomie, mineralogie, cimentation, structure du sol, microscopie electronique a balayage, rayons X a dispersion d'energie., 1. Introduction The effect of structure on the compressibility and shear strength of natural soils has been long recognized (e.g., Burland 1990; Leroueil and Vaughan 1990; Gens and Alonso 1992; [...]

This paper addresses the effects of cement treatment on the one-dimensional (1D) consolidation behavior of a highly organic soil (LOI ~ 40%-60%, where LOI is the loss on ignition), based on 1D constant rate of strain and incremental loading tests. The effects of Portland cement addition are evaluated for dosages ranging from 8% to 100% by dry mass of soil, corresponding to values of the cement factor of 24 and 296 kg of cement per cubic metre of untreated soil, within the range used in deep mixing practice. Additional parameters investigated are the impact of curing surcharge and duration. The most evident effect of the treatment is the development of a cementation-induced preconsolidation stress: the greater the cement dosage, the greater the preconsolidation stress and the greater the vertical effective stress that can be sustained at any void ratio. The results also provide a consistent picture of the effects of cement treatment on stiffness, hydraulic conductivity, coefficient of consolidation, and creep. Comparison to data obtained for the untreated soil demonstrates the 'stable' nature of the structure generated as a result of treatment. The consolidation results are complemented by pH measurements, extraction tests, elemental analyses, and Fourier transform infra-red (FTIR) spectroscopy analyses, which provide insight into the interaction between soil organic matter and cement. Key words: peat, organic matter, cement treatment, deep mixing, consolidation, creep. Cet article discute des effets du traitement au ciment d'un sol hautement organique (LOI ~ 40-60 %, ou << LOI >> est la perte au feu) sur son comportement en consolidation unidimensionnelle (1D), a partir d'essais en chargement en 1D a taux de deformation constant et incremental. Les effets de l'ajout de ciment Portland sont evalues pour des dosages variant de 8 a 100 %, ce qui correspond a des valeurs de facteur de ciment de 24 et 296 kg de ciment par metre cube de sol non traite, ceci etant des valeurs typiquement utilisees dans le melange en profondeur. Les parametres additionnels qui sont etudies sont l'impact de la surcharge durant le curage et sa duree. L'effet le plus evident du traitement est le developpement d' une contrainte de pre-consolidation induite par la cimentation : plus le dosage de ciment est elevee, plus la contrainte de pre-consolidation est elevee, et une plus grande contrainte effective verticale peut etre soutenue pour tout indice des vides. Les resultats fournissent aussi une image des effets du traitement au ciment sur la rigidite, la conductivite hydraulique, le coefficient de consolidation, et le fluage. Les resultats obtenus sont compares a des donnees provenant du sol non traite, ce qui demontre la nature << stable >> de la structure generee suite au traitement. Les resultats de consolidation sont complementes par des mesures de pH, des essais d'extraction, des analyses elementaires et des analyses de spectroscopie infrarouge a transformee de Fourier (<< FTIR >>). Ces analyses fournissent des informations sur l'interaction entre la matiere organique du sol et le ciment. Mots-cles : tourbe, matiere organique, traitement au ciment, melange en profondeur, consolidation, fluage. [Traduit par la Redaction], Introduction Peats and other soils high in organic matter are prone to large settlements, which derive both from their high compressibility and the significant impact of secondary consolidation. As a [...]

This paper addresses the one-dimensional compression behavior of a highly organic sapric soil in both its natural intact and reconstituted states, based on the results of constant rate of strain and incremental loading oedometer tests. The soil investigated contains 40-60% organic matter, comprised mainly of highly processed humic substances, and represents a 'transitional' material between inorganic clays and peats. The inorganic portion is entirely finer than 0.075 mm, with over 60% in the clay fraction ( DOI: 10.1061/(ASCE)1090-0241(2008)134:1(1) CE Database subject headings: Organic matter; Soil consolidation; Compression; Creep; Soil structure; Microscopy; Mineralogy.

This paper addresses the small-strain undrained shear behavior of clays based on an extensive testing program conducted on normally consolidated resedimented Boston blue clay (RBBC). The uniformity and reproducibility in the behavior of this soil permit a detailed study of the role of consolidation stress level, preshear consolidation stress path, preshear lateral stress ratio (K), rate of shear, and duration of laboratory aging on the small-strain ([[epsilon].sub.a] [less than or equal to] 0.1%) nonlinearity in undrained triaxial compression. The small-strain behavior of normally consolidated (NC) RBBC is measured using a LVDT-based device that is capable of resolving on-specimen axial strains smaller than 0.0001% strain over a 10% strain range, thus allowing full description of the small-strain nonlinearity. The testing program relies on a multistage testing approach developed to minimize specimen variability and reduce testing time. The small-strain nonlinearity of NC RBBC is found to be virtually independent of void ratio or stress level, all other testing conditions being equal. [K.sub.0]-consolidated RBBC presents the smallest linear region and the most rapid stiffness degradation (decrease in Young's modulus). Increases in K, strain rate and aging all cause a reduction in the small-strain nonlinearity of the soil. DOI: 10.1061/(ASCE)1090-0241(2007)133:1(72) CE Database subject headings: Clays; Young's modulus; Nonlinear response; Stiffness; Aging; Strain rate.

Tube sampling disturbance effects are investigated in this paper based on the results of constant rate of strain consolidation tests and unconsolidated undrained triaxial compression tests conducted on resedimented Boston blue clay sampled in the laboratory using a specifically designed device and employing various tubes differing in size, diameter to thickness ratio, and tip geometry. The effects of tube geometry were assessed based on comparison of the residual effective stresses, the reconsolidation strains, the undrained strength, and the one-dimensional drained compression behavior. Increasing degradation in the engineering properties was observed with decreasing diameter to thickness ratio (B/t), and the negative impact of a blunt tip geometry could not be compensated for even by a substantial increase in Bit. Comparison of these results to those obtained from triaxial element tests in which disturbance was simulated according to the ideal sampling approach (ISA), indicated that tube sampling is associated with far greater disturbances than what is accounted for by the ISA. Further, additional comparisons with the results of tests run on actual field samples of low over consolidation ratio Boston blue clay from two sites in the Boston area indicate that the behavior observed in the laboratory sampled soil is generally representative of actual field data. CE Database subject headings: Sampling; Clays; Shear strength; Simulation; Data analysis.