Vertical cyclic loading response of shallow skirted foundation in soft normally consolidated clay

Abstract

Skirted foundations are a potential foundation solution for a range of offshore structures, including hydrocarbon and renewable energy platforms and subsea structures. Offshore foundations can be subject to cyclic loading from environmental, installation, and operational events affecting the geotechnical response. A series of centrifuge tests have been performed on a shallow skirted foundation on normally consolidated kaolin clay under a range of vertical cyclic load sequences to investigate the effect of tensile or compressive average stress, the magnitude of the applied stress, and the effect of cyclic loading of low magnitude followed by consolidation on the foundation response. Results are presented as vertical foundation displacements normalized by the foundation geometry and interpreted within the traditional shear-strain contour approach. The findings indicate that the average, rather than maximum, vertical stress defines the foundation vertical displacement response and failure mode, a threshold stress exists below which a steady state is maintained even at a high number of cycles, and geotechnical resistance increases as a result of low-level cyclic loading followed by consolidation.

On the influence of drained cyclic preloadings on the cyclic behaviour of Zbraslav sand

“…The undrained cyclic stages were performed with a stress-controlled approach and considering a sinusoidal waveform, with amplitude of 𝑞 amp , loading frequency of 𝑓 = 0.1 Hz and period of T = 10 seconds. The selected loading frequency of 0.1 Hz correspond to typical offshore conditions [36,[56][57][58][59][60][61][62].…”

Vertical Monotonic and Cyclic Responses of a Bucket in Over-Consolidated Clay

“…For the bucket in sand over clay, the direction of w a was also governed by V a [25]. As for the bucket in clay, a few conventional [11,29] and centrifuge [30,31] model tests have been conducted. Given that the bucket was displaced under undrained conditions, the direction of w a and the failure mechanism were a function of the direction of V a : zero and tensile V a leaded to upwards w a , while compressive V a larger than a small level, for example, 9% of the monotonic vertical capacity, may always generate downward w a [31].…”

“…As for the bucket in clay, a few conventional [11,29] and centrifuge [30,31] model tests have been conducted. Given that the bucket was displaced under undrained conditions, the direction of w a and the failure mechanism were a function of the direction of V a : zero and tensile V a leaded to upwards w a , while compressive V a larger than a small level, for example, 9% of the monotonic vertical capacity, may always generate downward w a [31]. These phenomena of displacements were related to the positive excess pore pressure under compressive average loading and negative excess pore pressure under zero average loading [11].…”

“…At higher loading magnitudes, the accumulation of displacement was larger due to the more severe disturbance on soil. However, for loading magnitudes below a certain threshold, the bucket may be at a stable state without obvious residual displacement [31,32]. The displacement accumulated was observed under force-controlled loading, while the vertical resistance was degraded by about 35% in the first ~10 cycles and became stable at ~20 cycles if one-way cyclic loading with a small amplitude of ~0.009D was applied [33].…”

Undrained Pore Pressure Development on Cohesive Soil in Triaxial Cyclic Loading

“…The centrifuge tests on a shallow skirted foundation in normally consolidated kaolin clay have shown that two-way cyclic loading in average compression leads to continuous accumulation of the foundation settlement. The mode of failure for a skirted foundation under two-way vertical cyclic loading depends rather on the average vertical stress than on the maximal vertical stress [37].…”