Abstract
During pile installation into a submerged, sandy slope, liquefaction mechanisms including flow and cyclic liquefaction warrant attention. Because of the interconnection of these mechanisms, evaluating slope stability during and as a result of vibration-inducing construction activity is not trivial. This paper presents a practical approach to such an evaluation. The primary focus of any slope stability analysis must lie with flow liquefaction as the form of failure with the most hazardous potential. Given the importance of excess pore water pressure in giving rise to (delayed) slope failures due to cyclic loading events, excess pore pressure (EPP) generation and dissipation is the mechanism of most interest in modelling cyclic liquefaction. Currently, no engineering method exists which is able to capture the interconnected processes. Therefore, a hybrid model, consisting of a numerical tool which computes EPP generation and dissipation in time, is combined with empirical relations to describe the decay of EPPs generated due to pile driving in space and time. The proposed numerical tool predicts the evolution of EPP in a one-dimensional soil column close to a vibratory-driven pile, taking into account sustained static shear stresses, interim drainage, and pre-shearing. Radial EPP dissipation is considered the dominant mode of drainage. This engineering tool fits within a holistic slope stability analysis procedure, which is demonstrated for a submerged slope in the IJmuiden harbour of the Netherlands, where mooring piles and sheet piles are installed through a relatively loose layer of sand.
Highlights
In various civil, geotechnical, and offshore applications, piles or sheet piles are installed into fully saturated sands, for example during the foundation installation of offshore wind turbines
This paper presents a holistic and practical slope stability analysis procedure comprised of a combination of a soil strength framework and an approach for modelling liquefaction in slopes, taking into account empirically the redistribution of pore water pressure in space and time
Given the evident importance of excess pore water pressure in giving rise to slope failures due to cyclic loading events, excess pore pressure (EPP) generation and dissipation is the mechanism of most interest in modelling cyclic liquefaction due to pile installation
Summary
Geotechnical, and offshore applications, piles or sheet piles are installed into fully saturated sands, for example during the foundation installation of offshore wind turbines. Studies have been carried out which attempt to model the pore water response to pile installation or other vibrations related to construction in the near-field analytically (Randolph et al 1979), or in terms of a threshold densification model (Dobry et al 1981; Sawicki 1987; Matasović and Vucetic 1993); as well as redistribution of generated pore water pressure in time (Kokusho 1980; Malvick et al 2006), currently no engineering method exists which is able to capture the interconnected processes outlined, whilst allowing for an efficient evaluation to be made of the stability of a slope undergoing pile installation Under this consideration, this paper presents a holistic and practical slope stability analysis procedure comprised of a combination of a soil strength framework and an approach for modelling liquefaction in slopes, taking into account empirically the redistribution of pore water pressure in space and time.
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