V-H-Mcapacity of well foundations under gravity and seismic loading

Abstract

Well foundations are one of the most widely used deep foundations for bridges. As in case of other foundations, these foundations are also subjected to combined vertical force V, horizontal force H, and moment, M. In this research study, the geotechnical capacity of well foundation in frictional soil is determined under gravity and seismic loading condition, using 3D finite element limit analyses (FELA). Applicability of modelling of the well foundation as a rigid body, and effect of shape of bottom plug of the well, on the foundation capacity is also studied. Failure patterns at salient points along the capacity surface are identified and their characteristics are explained. Specifically, the location and shift in the position of point of rotation, for different combinations of H-M loading, are discussed in detail. A parametric study is also performed to identify the effect of vertical load, embedment depth ratio of foundation, soil strength parameters and seismic loading on foundation capacity. The capacity of the well foundation obtained using design methodology of Indian bridge design standards is also compared with the numerical results and a modification is proposed in the existing design methodology. The proposed methodology enables the designer to determine reasonably good estimate of the foundation V-H-M capacity.