Static and cyclic rocking on sand: centrifuge versus reduced-scale 1g experiments

Abstract

Shallow foundations supporting bridge piers, building frames, shear walls and monuments are often subjected to extreme lateral loading such as wind in offshore environments, or strong seismic shaking. Under such loading conditions, foundations may experience a host of non-linear phenomena: sliding on and uplifting from the supporting soil or even soil failure in the form of development of ultimate bearing capacity mechanisms. This type of response is accompanied by residual settlement and rotation of the supported structural system. Nevertheless, inelastic foundation performance can provide potential benefits to the overall seismic integrity of the structure. Thanks to such non-linearities, energy dissipation at or below the foundation level may eventually limit the seismic demand on structural elements. Several theoretical and experimental studies have provided encouraging evidence to this effect. This paper has a dual objective: first, to study the behaviour of shallow foundations under vertical and lateral monotonic loading and under lateral slow cyclic loading of progressively increasing amplitude; second, to explore the differences in foundation response between reduced-scale 1 g and centrifuge 50 g model testing. Emphasis is placed on interpreting their discrepancies by unveiling the role of scale effects. The role of soil densification due to multiple loading cycles with uplifting is also highlighted. Shallow foundations supporting bridge piers, building frames, shear walls and monuments are often subjected to extreme lateral loading such as wind in offshore environments, or strong seismic shaking. Under such loading conditions, foundations may experience a host of non-linear phenomena: sliding on and uplifting from the supporting soil or even soil failure in the form of development of ultimate bearing capacity mechanisms. This type of response is accompanied by residual settlement and rotation of the supported structural system. Nevertheless, inelastic foundation performance can provide potential benefits to the overall seismic integrity of the structure. Thanks to such non-linearities, energy dissipation at or below the foundation level may eventually limit the seismic demand on structural elements. Several theoretical and experimental studies have provided encouraging evidence to this effect. This paper has a dual objective: first, to study the behaviour of shallow foundations under vertical and lateral monotonic loading and under lateral slow cyclic loading of progressively increasing amplitude; second, to explore the differences in foundation response between reduced-scale 1 g and centrifuge 50 g model testing. Emphasis is placed on interpreting their discrepancies by unveiling the role of scale effects. The role of soil densification due to multiple loading cycles with uplifting is also highlighted.