Vertical bearing capacity of bucket foundation in sand overlying clay

- We perform axisymmetric analyses to determine the vertical bearing capacity of bucket foundations in sand overlying clay.
- Failure surface is revealed to be not unique and conditional on strength and geometrical parameters.
- Design charts and predictive equations for base capacity of bucket foundations are proposed.
- Proposed set of equations enhance the accuracy of base capacity compared with theoretical models.
- Shaft capacity can be estimated from an empirical equation for bucket foundations in uniform sand.

We perform a suite of axisymmetric finite element analyses to study the load transfer mechanism and predict the vertical bearing capacity of bucket foundations in sand overlying clay profiles. We use elasto-plastic soil models following Mohr-Coulomb and Tresca failure criteria for sands and clays, respectively. A non-associated flow rule is used with the Mohr-Coulomb model to realistically simulate the dilatant behavior of sands. A broad range of strength parameters for both sands and clays are used. The aspect ratio and bucket tip-to-clay depth (d) are also varied. The traces of plastic shear strain increments are monitored to observe how the vertical load is transmitted to underlying sand and clay layers, and to study the associated failure surface. The shape of the failure surface is shown to be not unique and display complex pattern conditional on strength parameters, aspect ratio, and d. We present a suite of equations to predict the vertical base capacity. The proposed set of equations provide enhanced estimate of the base capacity compared with theoretical models. We also calculate the shaft resistance of the bucket foundations on multi-layered profiles. The shaft resistance can reliably estimated from an empirical equation developed for bucket foundations in uniform sand.