Study On Bearing Capacity Of Shallow Strip Footings

Assuming the soil is an ideal plastic body and satisfies Mohr-Coulomb's yield criterion, three sections of the bearing capacity of shallow strip footings on Mohr-Coulomb soil are discussed in this paper.(1) The numerical computation of bearing capacity is done based on the slip-line theory and finite-difference method. Equilibrium differential equations of soil in the limit equilibrium state are deduced and the slip-line equations are got by the slip-line theory. Using the finite-difference method the computing program with the given boundaries is written out. It can compute the bearing capacity of shallow strip footings considering such parameters as the inclination of loads, the embedded depth and width of foundation, the internal frictional angle, the cohesion and the density of soil. The numerical results are compared with some classic results. The influencing factors on bearing capacity are discussed such as the width and embedded depth of foundation, the internal frictional angle, the cohesion and the density of soil.(2) The formula of bearing capacity considering the density of soil is got based on the slip-line theory. The assumption of the variable tendency of slip-line in active zone is made based on the numerical results. Combining the slip-line equations and boundaries, the formula of bearing capacity is deduced which can consider the density of soil. The formula of bearing capacity of strip footing on ponderable soil is also deduced assuming that the slip-line field of ponderable soil is the same with that of weightless soil, which is proved to be an upper-limit solution, as it's the same with that deduced by the upper-limit method in Prandtl mechanism.(3) The least upper-bound of bearing capacity is got based on the upper-limit method. Using the upper-limit method, the formula of upper-bound of bearing capacity is deduced in the velocity field, through which the least upper-bound is got. The computing program is also written out that can compute the least upper-bound of bearing capacity and the corresponding bearing capacity factors N_q N_c N_γ The numerical computing results are compared with other results including that computed by the slip-line method.