Effect of scale and spatial variability on surface foundation on sand

Abstract

This study aims to investigate the effect of scale and spatial variability on the bearing response of surface foundations on sand. Finite element analyses are performed using a generalized effective stress soil model, MIT-S, to investigate the scale effects in the foundation load response, under monotonic vertical settlement. Transitions in the mechanisms of ground deformations from general to punching modes are observed with changes in foundation size and sand void ratio. Model predictions of the bearing capacity factor, N[subscript gamma] are in good agreement with data reported from centrifuge model tests of circular and strip foundations on Toyoura sand. Further investigations are conducted to understand the effect of combined loading on circular footings on sand. Combinations of vertical, horizontal displacement and rotation are prescribed to foundation base to simulate different degree of load eccentricities and inclinations. Normalized failure envelopes describing allowable combination of vertical, horizontal and moment forces are established for different footing sizes and sand densities. Expansion of the failure envelope is associated with increased settlement depth and sand densities, while its rotation is affected by foundation size. Effect of spatial variability in sand density on the bearing response of circular footings on sands is also investigated. Random fields of sand void ratio are generated using a Karhunen-Loève expansion. A bounded-tanh function is used to characterize the statistical distribution of void ratio. Monte Carlo simulations are performed to establish impact of sand density variability and correlation length ratios on foundation bearing resistance. The stochastic predictions of N[subscript gamma] show that the mean bearing response is largely impacted by the statistical distribution of sand densities, but not by correlation lengths.