This work proposes a method for predicting the behavior of shallow footings bearing on an upper layer of processed cemented soil that overlies a lower layer of weakly bonded residual soil with a high void ratio. The paper describes the results of a series of field plate tests and numerical simulations. The results lead to a semi-empirical method for designing shallow foundations on a double-layer system. The method has been validated by comparison of predicted values with results from a separate series of plate-loading tests. For engineering practice, the proposed method provides acceptable predictions of bearing capacities and load-settlement curves.Key words: footings, cemented layer, layered system, weakly bonded, high void ratio.Résumé : Ce travail propose une méthode pour prédire le comportement de semelles superficielles portant sur une couche supérieure de sol-ciment fabriqué qui repose sur une couche inférieure de sol résiduel faiblement cohérent avec un rapport de vides élevé. Cet article décrit les résultats d'une série d'essais de plaque sur le terrain et de simulations numériques. Les résultats conduisent à une méthode semi-empirique pour la conception de fondations superficielles sur un système à double couche. La méthode a été validée en comparant les valeurs prédites avec les résultats d'une série séparée d'essais de chargement de plaques. Pour la pratique de l'Ingénieur, la méthode proposée fournit des prédictions acceptables des capacités portantes et des courbes charge-tassement.

Saturated drained triaxial compression tests with local strain measurement were carried out to evaluate the effects of using three different randomly distributed fibres (polyester,polypropylene and glass fibres) and rapid hardening Portland cement to improve the engineering behaviour of a uniform fine sand. In addition to the nature of the fibres,also analysed have been the separate and combined effect of fibre content (up to 0·5% by weight), fibre length (up to 36 mm), cement content (from 0% to 7% by weight) and initial mean effective stress (20, 60 and 100 kN/m2) on the deformation and strength characteristics of the soil. The present work searches for the establishment of a relation between the properties of the fibres and the mechanical behaviour of the composite material, originated from their combination with soil and cement. The cementation itself notably increased modulus, peak cohesive intercept, peak friction angle and brittleness of the sand. Inclusion of polyester and glass fibres (both relatively stiff) slightly reduced the stiffness and increased the peak friction angle of both the cemented and uncemented sand, and also slightly reduced the peak cohesive intercept and brittleness of the cemented composite. On the other hand,relatively flexible polypropylene fibre reinforcement dramatically reduced the brittleness (changing the mode of failure of the cemented sand from brittle to ductile for longer fibres) and stiffness, while increasing the ultimate strength of the cemented composite. Nous avons fait des essais de compression triaxiale drainéeet saturée avec des mesures de déformation locales afind'évaluer les effets de trois fibres différentes réparties sansordre (polyester, polypropylène et verre) et du ciment dePortland àdurcissement rapide pour améliorer le comportement industriel d'un sable uniforme fin. En plus dela nature des fibres, nous avons également analysél'effet séparé et combiné du contenu en fibres (jusqu'à0,5% en poids), de la longueur des fibres (jusqu'à 36 mm),du contenu en ciment (de 0% à7% en poids) et de lacontrainte effective moyenne initiale (20, 60 et 100 kN/m2)sur les caractéristiques de déformation et de résistance dusol. Cette étude cherche àétablir une relation entre lespropriétés des fibres et le comportement mécanique du matériau composite, venant de leur combinaison avec dusol et du ciment. La cimentation elle-même a nettementaugmenté le module, l'interception cohésive de pointe,l'angle de friction de pointe et la friabilité du sable.L'inclusion de fibres de verre et de fibres de polyester (toutes deux relativement rigides) a légèrement réduit larigidité et a augmenté l'angle de friction de pointe dusable cimenté et du sable non cimenté et a égalementlÉgèrement réduit l'interception cohésive de pointe et lafriabilité du composite cimenté. Par ailleurs, un renforcement relativement flexible àla fibre de polypropyléne aréduit la friabilité (changeant le mode de défaillance du sable cimenté de friable àmalléable pour les fibres plus longues) et la rigidité, tout en augmentant la résistance ultime du composite cimenté

This paper addresses the interpretation of loading tests bearing on a layered system formed by a compacted soil, coal bottom-ash and carbide lime top-layer overlying a compressible residual soil stratum. Load–settlement behaviour is observed from tests carried out using circular steel plates ranging from 0.30 to 0.60 m diameter on the top of a 0.15–0.60 m thick artificially cemented layer. Field data demonstrate the effectiveness of compacted soil–ash–lime layers in increasing bearing capacity and reducing foundation settlements where shallow foundations are used on weak residual soils. The paper also stresses the need to express test results in terms of dimensionless variables in plots of normalised applied pressure against settlement-to-diameter ratio. The efficiency of existing analytical solutions for layered cohesive-frictional soils in determining the bearing capacity of footings on processed cemented soil overlying a weakly bonded residual soil with high void ratio is evaluated.

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A busca por métodos sustentáveis de reforços em solos, proporcionou um estudo sobre a técnica de biocimentação, em solo arenoso. De acordo com estudos recentes sobre a biocimentação, há muito a ser estudado sobre a homogeneidade (MONTOYA et al., 2012), e em alguns estudos como o de (CHENG E CORD-RUWISCH, 2012) relatam a ocorrência de cimentação a certas profundidades, no entanto não apresentam dados da distribuição porosa na estrutura. Através destas considerações, esta pesquisa buscou analisar a homogeneidade de solo biocimentado, com areia de Osório/RS, construindo parâmetros para retratar a biocimentação no microtomógrafo a raio-x, modelo InspeXio SMX-90CT, da marca Shimadzu. Por ser um equipamento de analise não destrutiva, tornando sua análise de maior interesse para pesquisas que pretendem contribuir com estudo da técnica biocimentante. Obtendo com estas varreduras a distribuição da homogeneidade na estrutura biocimentada. Comparando os volumes de vazios com os laudos obtidos no microtomógrafo a raio-x, do solo composto por areia de Osório/RS, sem adição de agentes bioestimulante.