Validation of Foundation Design Method on Expansive Soils

Abstract

Nelson et al. (2015) presented design principles for foundations on expansive soils. The design principles consider free-field heave throughout the design life of a structure as the basis for foundation design. The design principles also consider water migration in the vadose zone, and the time required for subsoil wetting over the design life of the structure. This paper presents a method to validate the foundation design method presented in Nelson et al. (2015). The validation was performed using detailed long-term data obtained on a building constructed on expansive soils at the Denver International Airport, Denver, Colorado, USA. Water migration in the vadose zone and heave of floor slabs and drilled pier foundations were monitored over the time period from 2000 to 2016 and extended to a 25 year period (1991 – 2016) beginning at the end of construction. Water content profiles were modeled using VADOSE/W software, and heave of slabs and piers were computed using the design method presented in Nelson et al. (2015). The depth of wetting and changes in water content were used to compute heave according to the design method. Calculated heave was compared to the survey data. It was shown that the design method was capable of predicting heave to within 30 percent of the measured heave over a 25-year period.