Collaborative Research: Improving the Sampling and Characterization of Intermediate Soils

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Intermediate soils, which consist of varying mixtures of silts, clays, and sands, are common, naturally occurring deposits that can create design challenges for infrastructure projects involving dams, levees, highways, and building and bridge foundations. Geotechnical engineering practice is able to characterize clays and sands well, but it is the mixture of these two materials in combination with silt that can be particularly problematic. In some cases intermediate soils behave like clays and in others the behavior is like sands, and this uncertain transitional behavior violates the well-established knowledge base and standard of engineering practice used for clays and sands. The uncertainty in the characterization of intermediate soils forces engineers to be overly conservative (i.e., uneconomical) in the design of infrastructure projects to ensure the safety of society. This award supports research that will develop new methodologies for collecting intermediate soil samples by drilling and sampling, evaluating the quality of soil samples obtained, and accurately measuring their engineering properties in the laboratory for design of infrastructure. Outcomes from the research will provide practical guidance to the engineering profession leading to more reliable and economical design of infrastructure built upon intermediate soils. The project will also result in workforce development through the education and training of students and practicing engineers by incorporation of project findings into the classroom and professional short courses. The primary objective of this collaborative research project is to improve the understanding of how sampling influences the measured behavior of intermediate soils. The scope involves advanced triaxial testing that will simulate the sampling process, numerical modeling of the influence of various sampler geometries on sample state, creation of a conceptual sample disturbance framework, and implementation and validation of research findings at two field sites. The intellectual merit originates from three aspects: (1) research data and findings that will expand our knowledge of the effects of sampling on intermediate soils and their measured behavior; (2) formulation of a new conceptual framework that tracks the effect of sample disturbance on intermediate soils and creation of a corresponding new sample quality "index" parameter; and (3) development and validation via field testing of practice guidelines. The project will provide new scientific understanding and practical guidance that is urgently needed by the geotechnical engineering community. It is also anticipated that the research findings will be applicable to a broader range of materials, most notably fly ash, dredge materials, and mine tailings.