Dr John D. Nelson
Design of pier and grade beam foundations in highly expansive soils is one of the most important and challenging aspects of geotechnical engineering. Existing design methods consider only uniform soil profiles, and piers with limited length to diameter ratios. These methods are restricted with regard to evaluation of more complex aspects of pier heave. A finite element method of analysis was developed to compute pier movement in expansive soils having variable soil profiles, complex wetting profiles, large length-to-diameter ratios, and complex pier configurations and materials. The model has been named APEX (for Analysis of Piers in EXpansive soils). Dr. Nelson will describe the method of analysis and demonstrate its validity using several case histories. The results of pier design using APEX are compared with those of both conventional rigid pier analyses and elastic pier analyses. A series of simplified design charts developed using APEX are presented to facilitate its use. The results show the versatility of the model with regard to variable soil profiles and wetting zones.
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