Abstract
It is evident from model testing, field studies and theoretical considerations that the strength of a soft clay can reduce and then recover – potentially to above the initial value – as a result of cyclic loading followed by consolidation. For piled foundations and well conductors, these changes in soil strength and the resulting lateral resistance affect their stiffness, capacity and fatigue. This paper introduces a new model for the cyclic lateral ‘p-y’ response of a pile in soft clay, using concepts from critical state soil mechanics, combined with a parallel Iwan model to capture the hysteric response. Example analyses show that the model can capture the general forms of behaviour observed in model tests, and is rapid and simple to implement. The model provides a new basis for whole life modelling of piles and well conductors, allowing changes in stiffness and capacity to be simulated, as well as improved modelling of fatigue accumulation. This approach allows more reliable design, quantifying the benefits and risks associated with evolving soil strength.
Highlights
Pile foundations and oil and gas well conductors rely on lateral support from the soil to resist horizontal loads
Model tests of ‘episodic’ cyclic loading – i.e. with sets of cycles interspersed by periods of consolidation – by Zhang et al (2011) showed the pile head lateral stiffness fall to 40% of the initial value during an initial cyclic episode, but rise by a factor of 2 following subsequent consolidation periods
This paper sets out a new p-y model for the long term ‘whole life’ behaviour of laterally-loaded piles in soft clay
Summary
Pile foundations and oil and gas well conductors rely on lateral support from the soil to resist horizontal loads. The part of a well conductor immediately below the seafloor acts as a laterally-loaded pile that provides restraint for the well sections below and above. It is con ventional for the soil reaction on piles and conductors to be reduced to a single degree of freedom ‘p-y’ non-linear spring, which describes the lateral resistance offered by the integrated effect of the soil around the pile. For laterally-loaded piles, modifications to the monotonic p-y response have been proposed to allow for the effects of cyclic loading, which generally involve a factoring down of the static lateral resistance More sophisticated methods exist to convert a history of cyclic loading into a specific p-y response (Erbrich et al 2010, Zhang et al 2017, Komolafe and Aubeny 2020)
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