An important type of geotechnical composite system incorporates columns of strong material installed in soft clay, with an overlying layer of coarse-grained soil that may include geosynthetic reinforcement. The purpose of the overlying "bridging" layer is to transfer loads from embankments or structures into the columns, thereby reduceing differential settlements. Existing design methods for such systems provide widely-varying requirements for geosynthetic reinforcement, and there is no consensus regarding which of these methods, if any, is accurate. Furthermore, none of the existing methods provide means for predicting differential settlement magnitudes. This research will include (a) pilot-scale tests of square and round columns moving up into a geosynthetic-reinforced soil layer; (b) new data collection from two contemporary, full-scale field installations, (c) three-dimensional mathematical analysis of the behavior of geosynthetic reinforcement layers considering orthotropy, orientation, and stress concentrations, and (d) three-dimensional numerical analysis of the entire geotechnical composite system. These tasks will be coordinated to determine the effects of the important system parameters, including: the layout, spacing, diameter, stiffness, and strength of the columns; the size and shape of caps on top of the columns; the material properties, depth, orientation, and ultimate strength of the geosynthetic layer(s); the properties of the bridging layer above the columns; the properties of the soft clay between the columns; the depth of the bridging layer; the interface behavior at the top and bottom of each geosynthetic layer; and the surface loading.
The broader impacts of this research include the development of tools for more economical and reliable design of foundation systems for transportation embankments and structures. The investigators will engage minorities, women, and undergraduates in their research. They will involve interested individuals, committees, and organizations from the U.S. and international community in the research, and they will promote communication, networking, and partnerships related to geotechnical composite foundation systems incorporating columnar support and geosynthetic reinforcement.
