Three-dimensional Study of Gravels

University Of Washington, Seattle WA

Investigators

Abstract

Gravels and gravelly soils are engineering materials commonly used in many civil engineering applications such as structural fills and pavement subgrades. The geotechnical engineering community has long known that gravels have engineering properties that are both similar and non-similar to sands. Sands have been researched extensively, for both static and dynamic loading conditions, and their behavior is comparatively well understood. In contrast, gravels have been researched and tested to a much lesser extent due to the need for large specimen sizes and physical difficulties of handling such specimens. Consequently, the engineering properties of gravels have been commonly obtained by means of correlations based on experimental tests on sands. In addition, granular material behavior understanding is primarily based on conventional triaxial tests where specimens are tested under axisymmetric principal stress conditions. These particular stress conditions apply only for special situations in engineering practice, such as soil lying directly below and on the axis of a circular load. Often, conditions exist where none of the principal stresses are equal. It is then necessary to take into consideration the influence of the intermediate principal stress on the stress-strain and strength characteristics of the material. During the last three decades, much research has been conducted on the behavior of sands under multiaxial, or true, states of stress. Cubical triaxial devices, that allow the intermediate principal stress to vary from the minor to the major principal stress, have facilitated research on the behavior of sands, clays, rock and concrete in three-dimensional principal stress space. Missing from the literature is any comprehensive study focusing on multiaxial testing of gravel-sized particles. In an effort to address this gap in fundamental understanding of gravelly soils, an extensive study of several gravels under three-dimensional stress paths is proposed. Based on a systematic experimental program using a flexible boundary true triaxial device, the three-dimensional behavior of gravels will be ascertained. The effects of grain size, particle shape, and fines content on the mechanical response of gravels will be evaluated. The device boundary effects will be evaluated using new instrumentation that will be developed as part of the project. A constitutive model for gravels will be developed and calibrated from preliminary experimental data and verified against further test results. The calibrated model may enable successful numerical modeling and performance prediction of Civil Engineering geotechnical structures and foundations.