A series of undrained monotonic triaxial compression tests were performed on Ottawa sand containing 0%, 5%, 10% and 15% of non-plastic silt. The paper focuses on distinctive states of the monotonic undrained response of sands, namely the critical state, the phase transformation state, the quasi-steady state, and the state of undrained instability (onset of flow liquefaction). Specimens were prepared using slurry deposition and moist tamping to investigate the effect of the initial sand fabric on these states. It was observed that an increase in the non-plastic fines content leads to a downward shift of the critical-state line in the void ratio–mean effective stress space and to an increase of the critical-state friction angle. The present data suggest that the initial fabric of the sand appears to have a significant effect on the undrained behaviour in the early stages of shearing, with its influence vanishing at large strains. Moist-tamped specimens demonstrate considerably larger undrained instability state strength than their slurry-deposited counterparts, and a unique critical state locus is reached by both moist-tamped and slurry-deposited specimens. A mathematical formula that allows the estimation of the mean effective stress at the phase transformation state based on the initial mean effective stress and void ratio is also proposed.

The finite element method is used for the determination of the collapse load of a rigid strip footing placed on a uniform layer of purely frictional soil subjected to inclined and eccentric loading. The footing is set on the free surface of the soil mass with no surcharge applied. The soil is assumed to be elastic – perfectly plastic following the Mohr–Coulomb failure criterion. Two series of analyses were performed, one using an associated flow rule and one using a nonassociated flow rule. The first series is in accordance with bearing capacity solutions currently used in shallow foundation design practice, while the second one is consistent with the dilatancy exhibited by sands in reality. Both probe-type analyses and swipe-type analyses were undertaken. Analyses for associated and nonassociated flow rules yield essentially the same trends regarding the effective width, inclination factor, and normalized vertical force – horizontal force – moment (V–H–M) failure envelope. The results show that the inclination factor depends on the value of the friction angle, whereas the effective width does not.

The paper examines, using numerical modelling, the problem of the limit shaft resistance of non-displacement piles installed in sands. The modelling makes use of an advanced, two-surface-plasticity constitutive model. The constitutive model predicts the soil response in both the small- and the large-strain range, while taking into account the effects of the intermediate principal effective stress and of the inherent anisotropy of the sand. Finite element analyses of shearing along the pile shaft are performed in order to examine the development of limit unit shaft resistance and the changes in stress state around the shaft upon axial loading of the pile. Special focus is placed on the operative value of the lateral earth pressure coefficient when limit shaft resistance is reached. The analyses offer useful insights regarding the factors controlling the value of unit shaft resistance in sands. The simulations predict a significant build-up of horizontal effective stress for dense sands. Based on these simulations, we propose a relationship between the lateral earth pressure coefficient for use in the calculation of the limit shaft resistance of the pile and the initial density and stress state of the sand.