Abstract
The response of pile groups and piled structures to vertical and tunnelling-induced loads is studied. A two-stage model is adopted that can efficiently consider external actions, greenfield tunnelling movements, superstructure stiffness, ultimate pile shaft and base stresses, pile-soil interactions in uniform or layered soils, and local soil behaviour (as either linear elastic, elastic perfectly-plastic, or nonlinear). Several scenarios are analysed: namely, piles subjected to vertical loads; piles and piled structures that are affected by tunnelling induced ground movements. Model results for piles under vertical loads compare well with field and other analytical models, confirming the robustness of the model. For tunnelling adjacent to or beneath single piles and pile groups, the impact of layered soils, soil yielding, and hyperbolic transfer mechanisms are shown to be significant, indicating that these aspects should be considered in risk assessments when using simplified models. Analyses of tunnelling beneath free-head piles and piled equivalent beams (describing flexible slabs or stiff buildings) confirm that pile-foundation connections and superstructures decrease tunnelling-induced displacements and deformations at the surface level; however, their action can also worsen the foundation distress with respect to force-moment structural capacity. Considering that the envelopes of fully-flexible and perfectly rigid superstructures will not always be conservative, soil-pile-structure interaction models are recommended for design.
Highlights
The behaviour of piles under static loading has been a subject of practical research for several decades
For tunnelling adjacent to single piles and to pile groups, accounting for the limit forces at the shaft and base, and for the soil stiffness degradation, provides more realistic predictions of tunnelling-induced pile forces and settlements, which depend on greenfield movement magnitude and pre-tunnelling loads
Layered ground conditions play a role in the tunnel-pile-structure interaction, the nature of which depends on the type of load-transfer mechanism adopted for the soil-pile interface; engineering judgement is needed when applying lessons from previous studies on tunnel-pile interactions in uniform soil to real cases with layered grounds
Summary
The behaviour of piles under static loading has been a subject of practical research for several decades. Elastic perfectly-plastic (Basile, 2014), hyperbolic (Korff et al, 2016), and tri-linear (Dias and Bezuijen, 2018a) load-transfer mechanisms have been used for isolated piles affected by tunnelling, continuum-based models of pile groups considering pileto-pile interaction (in which the soil stiffness matrix is obtained from half-space theory, as opposed to approximated Winkler models) are mostly limited to linear elastic soil behaviour (Loganathan et al, 2001; Xu and Poulos, 2001), for layered grounds (Huang and Mu, 2012; Mu et al, 2012). This paper aims at exploring the nonlinear response of pile groups and piled structures to external (active) and tunnelling-induced (passive) loads using a proposed two-stage model named COMPILE, which is designed for practical use due to its computational efficiency This model, implemented as a Matlab code, conducts a fully coupled analysis of the soil-foundation-structure system, considering both yielding and hyperbolic local stiffness degradation of the soil. The EL equations can be solved directly, whereas the EP and NP solutions require an incremental and iterative procedure (for both Stages 1 and 2)
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