Estimation and engineering application of bearing capacity factors (N_c) in clay strata under undrained condition

In order to consider the effect of shape and depth of foundations in estimation of bearing capacity of foundation soils and stability analysis of excavations, an approximate analytical method to calculate the bearing capacity factor N_c is proposed. According to this method, the estimation of bearing capacity of foundations with different shapes and depths can be unified into the same equation. If the depth of the plastic zone is properly modified, the calculated results will be very close to those from the laboratory test data and the field investigations. It was proven by this method that the value of N_c in the calculation of bearing capacity is identical to that in the analysis of excavation stability. On the basis of the method, the influence of embedment depth of the enclosure structure can be taken into account in the Terzaghi's method for analysis of the stability against heave of excavations. Moreover, an approximate approach to estimate the bearing capacity factors of shallow foundations is also put forward.