Deep Undrained Bearing Capacity of Rectangular Foundations in Uniform Strength Clay

Abstract

The deep vertical bearing capacity of rectangular foundations of varying aspect ratios (0.2–10) are explored within a coupled Eulerian–Lagrangian (CEL) finite element modeling framework. The CEL model is verified against existing numerical and theoretical solutions. For accurate shallow bearing capacity assessment, large deformation finite element (LDFE) solutions were found to be suitable if penetration resistance is extracted at normalized penetration depths of less than 5% of the foundation width. The deep bearing capacity factor for a circular foundation was predicted within ∼2% for a smooth foundation and ∼5% for a rough foundation. Soil weight and stiffness were found to have no impact on the penetration resistance at shallow depths but to influence the resistance at deeper depths. The relative foundation thickness has a profound influence on the deep bearing capacity factor (Nc). Increasing the normalized foundation thickness from 0.1 to 0.5 increased the bearing factor by more than 20%. An alternate soil flow mechanism was discovered responsible for this increase. The deep bearing capacity factor for a rectangular foundation was found to nonlinearly increase with the footing aspect ratio. An exponential form of equation was shown to capture well the effects of varying aspect ratio and footing thickness. The effect of the common assumption of a rigid foundation on bearing capacity in geotechnical numerical analyses has been revisited.