Soil behavior under low- and high-cycle loading—Element tests vs. constitutive models

https://doi.org/10.1016/j.gete.2020.100188Get rights and content

Highlights

  • Strain accumulation is affected by grain size distribution, grain shape and fabric.

  • Multiple polarization changes have rather small effect on strain accumulation.

  • Monotonic loading phases may delete the cyclic preloading memory.

  • Data bases with undrained cyclic tests on fine sand and kaolin are presented.

  • Constitutive models work well for certain test types and show deficits for others.

Abstract

The first part of the paper deals with high-cycle loading and presents a parametric study with numerous drained cyclic tests with a large number of cycles (N104). The dependence of the strain accumulation rate on initial relative density, amplitude, average stress and cyclic preloading is addressed. These test series form the basis of the calibration of a high-cycle accumulation (HCA) model, which is briefly explained. Furthermore, the influences of the grain size distribution curve, particle shape and the sample preparation method on the cumulative strains are discussed. In further test series the effects of multiple changes of the direction of the cycles, of frequently changing amplitudes, and of changes of the average stress between bundles of cycles were investigated. The second part of the paper is dedicated to low-cycle loading. A data base with a large number of undrained cyclic triaxial tests performed on a fine sand is presented. The test conditions comprise stress or strain-controlled cycles, performed from isotropic or anisotropic initial stresses and involving different densities and amplitudes. The predictions of three sophisticated constitutive models for sand, namely hypoplasticity with intergranular strain, ISA and Sanisand, are tested against the experimental data. Finally, a second data base concerning a large number of cyclic tests on kaolin is briefly introduced.

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 (N>103) of relatively small strain amplitude (εampl<103) 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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