Pile driving and submarine slope stability: a hybrid engineering approach
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P. Lamens I A. Askarinejad
Pile driving and submarine slope stability: a hybrid engineering approach
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. Keywords Pile driving . Coastal slope stability . Liquefaction . Flow slides . Vibrations
Notations EPP CSL CSRL CSR CRR SSR IL ESP, TSP TRX, DSS β h N Nliq Id ψ δ p, p′ q u ru
Excess pore pressure Critical state locus Constant stress ratio line Cyclic shear stress ratio Cyclic resistance ratio Static shear stress ratio Instability line Effective, total stress path Triaxial, direct simple shear Slope angle Slope height No. of loading cycles Loading cycles to liquefaction Relative density State parameter Friction angle soil-pile interface Total, effective isotropic stress Deviatoric stress Pore water pressure Relative excess pore water pressure
σij, σ′ij K η τ εij γ G ν α e cv, cr su ϕ′ r
Total, effective stress component Coefficient of lateral earth pressure Stress ratio q/p′ Shear stress Strain component Shear strain Shear modulus Poisson’s ratio Rotation of principle stress axes Void ratio Vertical, radial consolidation coefficient Undrained shear strength Effective friction angle Radial distance
Introduction 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. Another common case is installation of (mooring) piles into submerged slopes along harbour or port embankments. A
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