Design Procedure and Considerations for Piers in Expansive Soils

Abstract

The design of pier foundations in expansive soils is an important and challenging aspect of geotechnical engineering. Established methods for pier analysis include rigid and elastic methods. These methods have certain limitations that restrict their applicability to evaluate certain complex aspects of pier heave, including variable soil profiles, complex wetting profiles, large length-to-diameter ratios, and complex pier configurations and materials. To address those limitations, a method of analysis was developed providing a versatile and robust tool to predict both pier heave and axial forces developed by expansive soils. This method utilizes a standard finite-element code to solve for pier heave and force in the pier for the given boundary conditions. This paper contains both a discussion of the general design procedure and the finite-element formulation. This design procedure, including the finite-element code, accurately determines pier heave and force in a pier compared with field-measured data. The design procedure and the finite-element code in particular, address the limitations of the established rigid and elastic pier analysis methods with the flexibility to evaluate complex design situations. A comparison with field-measured pier heave and tensile force in the pier demonstrates that the design procedure accurately models both the magnitude of pier heave and force in the pier. The results obtained using this design procedure have been compared with those obtained using the established pier analysis methods for simplified drilled pier examples. The comparison of the various methods of analysis demonstrates that the finite-element design procedure predicts pier heave values that are generally less than the existing elastic and rigid pier analysis methods. It is believed that the proposed design method is more realistic and provides a design tool with improved accuracy compared with existing methods.