Soil behavior under low- and high-cycle loading—Element tests vs. constitutive models
Introduction
Cyclic loading is of practical relevance to many problems in geotechnical engineering. Cyclic loading of non-endogenous nature may be caused by traffic (high-speed trains, magnetic levitation trains), industrial sources (crane rails, machine foundations), wind and waves (on-shore and off-shore wind turbines, coastal structures) or repeated filling and emptying (locks, tanks and silos). Furthermore, construction processes (e.g. vibration of sheet piles) and mechanical compaction (e.g. vibratory compaction) introduce cyclic loads into the soil. Cyclic loading may be also caused by endogenous sources, e.g. by the shear wave propagation during earthquakes.
Repeated loading that involves a large number () of relatively small strain amplitude () cycles is referred to as high-cycle loading. Offshore wind turbine foundations under wind and wave action and infrastructure under traffic offer typical examples. In contrast, cyclic shearing caused by high intensity earthquakes usually involves a lower number of cycles, but with potentially larger strain amplitudes and significant relaxations of in situ effective stresses being caused by the cycles.
This paper summarizes the results from experimental laboratory studies that focus on both high- and low-cycle loading.
Section snippets
High-cycle loading of sand
Most of the tests with high-cycle loading of sand discussed in the following have been performed in the context of the high-cycle accumulation model proposed by Niemunis et al. 1 The procedure in finite element calculations with this model and the main equations are summarized in the Appendix.
Low-cycle loading of coarse-grained soils
The following paragraphs present data from numerous undrained cyclic triaxial tests performed with various boundary conditions on Karlsruhe fine sand.34,35 These data are freely available electronically from Ref. 36 and may be used to develop, check and calibrate constitutive models that focus on low-cycle loading. The identity codes of most of the tests given in the following sections are as defined in Refs. 34, 35. Those tests that were not included in the Refs. 34, 35 database are not given
Summary and conclusions
The rates of strain accumulation developed in sand triaxial specimens under high-cyclic loading grow with increasing stress or strain amplitude, decreasing density and increasing average stress ratio. At similar density and loading conditions, finer and more well-graded sands show higher cumulative strains. Tests on glass beads, natural sand and crushed sand demonstrated influences of grain shape that depend on stress level. At low pressures, materials with round particles show considerable
CRediT authorship contribution statement
T. Wichtmann: Conceptualization, Methodology, Investigation, Validation, Visualization, Writing - original draft, Writing - review & editing, Supervision, Project administration, Funding acquisition.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Parts of the research presented in this paper were performed within the framework of the project ”Improvement of an accumulation model for high-cyclic loading” funded by German Research Foundation (DFG , project Nos. TR218/18-1/2, WI 3180/3-1/2). The author is grateful to DFG for the financial support. Most of this research were done during the author’s former engagement at the Institute of Soil Mechanics and Rock Mechanics (IBF) at Karlsruhe Institute of Technology (KIT). The majority of the
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