Abstract Soft ground improvement techniques have evolved substantially in Brazil in recent years. However, their application in soft and very soft clays requires a good understanding of the fundamentals of ground improvement techniques suited to the problem as well as the actual field behavior when implemented on a real scale. This paper describes some of the most widely used ground improvement techniques in the context of very soft clays in Brazil. The techniques described in the paper use prefabricated vertical drains (PVD) such as vacuum preloading; or combine PVD and rigid inclusion, such as CPR grouting; or are purely column-like elements such as piled embankments (including those executed with the deep mixing technique, DSM); or combine column-like elements with the drainage function, such as stone columns and geosynthetic encased columns; or use cementitious binders such as shallow soil mixing. The paper reference condition is a soft clay foundation in which no strengthening is implemented, such as, an embankment with basal reinforcement or soft clay with vertical prefabricated drains, or the use of vacuum preloading to speed up the consolidation rate. The applications of the ground improvement techniques are illustrated by case histories, numerical analyses, or physical models. Different types of measurements are used to evaluate the performance of each technique, including settlements, horizontal displacements, excess pore pressures, embankment applied stresses, stress concentration factors, and clay strength following the ground treatment. The settlement improvement factor β, the ratio between the settlements for untreated and treated conditions, is shown to be a suitable parameter to assess the degree of improvement imposed in the soft foundation by ranking the various methods in increased order of strengthening effect.

RESUMEN Os principais aspectos geotécnicos da Formação Solimões no estado do Acre para a área de pavimentação rodoviária são: a escassez de pedras britadas, os elevados índices de precipitação e a ocorrência generalizada de solos expansivos ao longo do subleito. A alta variação volumétrica desses solos vem causando prejuízos financeiros e dificultando o transporte terrestre na região. Embora a maioria dos solos locais seja predominantemente composta por argilominerais com estrutura 2:1, a influência do comportamento desses solos em obras de pavimentação ainda é pouco estudada na região. Este artigo avalia 05 amostras de solos potencialmente expansivos coletados nos arredores da cidade de Rio Branco. São realizados, em amostras deformadas, os ensaios de caracterização física, Microscopia Eletrônica de Varredura, difratometria de raios-X, espectrometria de fluorescência de Raios-X e de absorção de azul de metileno. Por meio de correlações existentes, os resultados evidenciam o elevado potencial de expansão das amostras e a importância de um estudo e mapeamento mais abrangente que auxilie o meio técnico local em obras rodoviárias.

ABSTRACT The main geotechnical aspects of the southwestern Brazilian Amazon are the absence of rocky outcrops to provide gravel for road construction, the widespread occurrence of expansive soils along the road subgrade and high rainfall indices. The high volumetric changes of these expansive soils has been causing huge financial losses. Although most of the local soils are rich in 2:1 clay mineral, the understanding on how the behavior of these materials influences local pavements is still very limited. This paper asses 05 disturbed expansive clays samples of Rio Branco city. Physical, chemical and mineralogical characterizations are presented. The laboratory tests are then combined with traditional empirical correlations in order to evaluates the expansiveness of Rio Branco clays. The results showed the high swelling potential of the samples and the need of more studies that provides a clear understanding of these expansive clays.

RESUMO Esse artigo apresenta os resultados experimentais da avaliação das características mineralógicas de um tipo de solo característico do estado do Acre – localmente conhecido como tabatinga – na confecção de agregados artificiais de argila calcinada visando seu emprego em camadas de bases de pavimentos rodoviários. A correta identificação dos argilominerais através da técnica de Difração de Raios X se mostra mais confiável e eficaz quando precedida de tratamentos preliminares da amostra envolvendo sedimentação, retirada de ferro e preparo de lâminas em condições saturadas e aquecidas. Os resultados indicam que o solo apresenta características mineralógicas compatíveis com a produção de agregados calcinados com características físicas e mecânicas adequadas para o uso proposto, além de indicar que os critérios de classificação preliminares envolvendo índices físicos nem sempre são suficientes.

ABSTRACT This paper presents the experimental results of the evaluation of the mineralogical features of a soil from the Southwest of the Brazilian Amazon used to produce calcined aggregates for road pavements. The identification of clay minerals by X-Ray Diffraction technique is more efficient when preceded by preliminary sample treatments involving sedimentation, iron removal and preparation of microscope slides under glycol-saturated and heated conditions. The results show that the soil presents mineralogical features suitable for the production of calcined aggregates with acceptable mechanical behavior for the proposed use; they also show that the preliminary classification involving physical indexes are not always sufficient to verify the suitability of the soils.