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Undrained cyclic loading of normally consolidated clays, interspersed with consolidation (i.e., episodic cyclic loading), has been shown to lead to softening followed by hardening, manifested by evolving parameters such as strength, stiffness, and coefficient of consolidation. The current evidence base is drawn from tests in which soil strength has been fully mobilized in each cycle of loading, whereas in practice, changes in stress around a geotechnical infrastructure typically occur only at a prefailure level. This paper presents results from a set of stress-controlled episodic cyclic direct simple shear tests imposing prefailure stress reversals in each cycle. Differences in soil response are identified for the same total number of cycles of loading but imposed through packets of different numbers of cycles and, consequently, different numbers of intervening consolidation stages. The results highlight the effect of load history on operational soil properties and quantify the effect of the undrained prefailure cyclic loading history on the evolution of the soil properties, supporting the application of whole-life geotechnical design in practice.

Introduction

The global energy industry is going through a significant period of transition aiming to net zero greenhouse gas emissions in the coming decades, and renewable energy is expected to be one of the fastest-growing energy sources globally (International Energy Agency, 2021).

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