Design of Shallow Foundation considering Site-Specific Rainfall and Water Table Data: Theoretical Framework and Application

Abstract

The increase of significant hydrological events, such as heavy rainfall and flooding, in recent years has adversely impacted the performance of many structures, particularly the foundations that transfer the superstructure load to the ground. The shear strength and settlement of soils and foundations are all influenced by the degree of saturation of the soil, which varies with hydrological parameters, such as rainfall, and subsurface parameters, such as the water table depth. Therefore, in addition to the traditional geotechnical parameters, the hydrological parameters must be incorporated in the design to obtain the optimum design and to understand the impacts of hydrological parameters on the bearing capacity and settlement of shallow foundation for a particular location. In this study, a novel procedure, which considers the site-specific historical rainfall and water table data in the shallow foundation design, is presented with sample applications to two sites in the US. The degree of saturation of partially saturated soil within the influence zone of the foundation was modeled using the one-dimensional Richards’ equation considering infiltration rate and water table location as the top and bottom boundary conditions, respectively. The historical rainfall data and water table locations for the two study areas of Victorville, California, and Levelland, Texas, were obtained from the USGS and National Climatic Data Center (NCDC) data repositories. The results from the Victorville site indicated a near 230% increase in the ultimate bearing capacity and a corresponding 87% decrease in the elastic settlement from those calculated assuming the fully saturated condition. On the other hand, there was only a small increase in bearing capacity at the Levelland site with a corresponding decrease in settlement of 49%. The results clearly indicated that the performance of shallow foundation can be better predicted if the hydrological parameters are incorporated into the current design procedure.