A probabilistic approach to the ultimate capacity of skirted foundations in spatially variable clay

Abstract

Newcastle University ePrints -eprint.ncl.ac.uk Charlton TS, Rouainia M. A probabilistic approach to the ultimate capacity of skirted foundationsin spatially variable clay. Structural Safety 2017, 65, 126-136. AbstractSkirted foundations are used in offshore applications to resist the large horizontal and moment loads that are characteristic of the ocean environment. The combination of vertical-horizontalmoment (VHM) loading results in complicated stress conditions in the seabed and design is often based on VHM failure envelopes. These have generally been constructed by numerical analysis using a deterministic characterisation of soil properties and disregard the natural spatial variability of marine sediments. In this study, spatial variability is taken into account by coupling a random field model with finite element analysis. The paper presents a probabilistic analysis of the ultimate capacity of skirted foundations in spatially variable undrained clay. The increase of strength with depth typical of a marine clay is included in the modelling framework.Probabilistic failure envelopes are constructed to analyse the effect of spatial variability when skirted foundations are subjected to different combinations of VHM loading. The results show that the probability of failure increases under high vertical loads and at peak moment capacity in the HM plane, suggesting that care should be taken in design at these areas of the failure envelope. The methodology demonstrates a straightforward and effective way of quantifying uncertainty in the ultimate limit state design of offshore geotechnical structures and the results presented provide specific guidance for the design of skirted foundations.

Variabilidad espacial del suelo arcilloso de la Sabana de Bogotá en la confiabilidad de asentamientos por consolidación primaria

“…Aun así, dicha recopilación no presenta todos los paráme-tros de consolidación de este estudio y relaciona datos de diversos orígenes sin indicar la representatividad de los mismos para aplicar en todos los trabajos de diseño ingenieril. De esta manera, se calcularon los valores de COV para cada uno de los parámetros de consolidación del suelo del sector Sabana Centro de la Sabana de Bogotá en función del número de ensayos (Figura 8), tal como lo propone Charlton y Rouainia [33]. La Figura 8 se obtuvo mediante el cálculo de COV conforme aumentó el número de ensayos u observaciones; es decir, se estimaron los valores de µ y σ desde el ensayo 1 hasta el ensayo 30 y, simultáneamente, se obtuvo el COV para los ensayos acumulados.…”

Probabilistic failure envelopes of strip foundations on soils with non-stationary characteristics of undrained shear strength

“…The definition of probabilistic failure envelopes in this study follows that described by Charlton and Rouainia (2017). The probabilistic failure envelope corresponding to a given probability level p refers to a failure envelope consisting of a series of the quantile of failure loads Fu,p with level p in varying loading directions.…”

“…The size and shape of failure envelopes can be investigated and compared in the dimensionless and normalised loading spaces, respectively. The size of probabilistic failure envelopes has been investigated for shallow foundations on soil characterised by both stationary (Cassidy et al, 2013;Hentati et al, 2018) and non-stationary (Charlton & Rouainia, 2017) random fields.…”

“…3b (Yi et al, 2020). Charlton & Rouainia (2017) explored probabilistic failure envelopes of skirted foundations on soils represented by a non-stationary random field, but neglected variation of undrained shear strength at the mudline su0 (i.e., σsu = 0 at z = 0, see Fig. 3c) such that horizontal capacities of surface foundations are nearly constant irrespective of soil spatial variability.…”

Uplift Behavior of Pipelines Buried at Various Depths in Spatially Varying Clayey Seabed

“…Frequently, the spatial distributions of soil properties are treated as a random field and several random finite element analyses have been undertaken to explore the responses of offshore structures in spatially random soils. Charlton and Rouainia [19] undertook a probabilistic analysis on the bearing capacity of skirted foundations under combined vertical-horizontal-moment loadings and constructed several probabilistic failure envelopes. Cheng et al [20] carried out a large deformation random element analysis to investigate the uplift responses of helical anchors in random clay, and the failure mechanisms and pullout capacities of anchors under different statistical characteristics are extensively analyzed.…”