Calculation of heave of deep pier foundations
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.
Dr. Nelson has over 45 years of experience in the areas of consulting engineering, research, teaching, and construction. He was on the faculty of Colorado State University for 39 years. During that time he was also an original shareholder in Shepherd Miller, Inc. after which he served as a corporate consultant at Tetra Tech, Inc. for 7 years. He is currently a Principal and owner of Engineering Analytics, Inc. Dr. Nelson is the senior author of the text reference book, “Expansive Soils, Problems and Practices in Foundation and Pavement Engineering.” Since 1974 he has been actively engaged in research and practice dealing with slabs and foundations on expansive soils. He was the principal investigator on several major research projects to investigate water movement in expansive soils and developed methods of heave prediction beneath slabs. He also conducted research on full-scale piers in expansive soils. He has provided professional litigation support dealing with slabs and foundations on expansive and collapsing soils. He collaborated on the development of a FEM method to calculate heave of piers in expansive soil. He is the author of more than 100 technical papers and reports.
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