Cyclic and creep combination effects on the long-term undrained behavior of overconsolidated clay
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RESEARCH PAPER
Cyclic and creep combination effects on the long-term undrained behavior of overconsolidated clay Jian Han1 • Zhen-Yu Yin2 • Christophe Dano3 • Pierre-Yves Hicher4 Received: 26 January 2020 / Accepted: 12 September 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Soft soil subjected to cyclic loading typically exhibits an increase in excess pore pressure under undrained condition which brings the soil to an overconsolidated state. Then, under a subsequent large number of cycles (e.g. more than one million) which also takes time, the creep at overconsolidated state influences the cyclic effect and thus results in a complicated longterm undrained behavior. This paper aims to clarify this long-term undrained behavior of overconsolidated clay. The reconstituted samples are prepared from natural samples retrieved in the north of France. First, the shear strength characteristics along monotonic triaxial stress paths are identified. Then load control cyclic tests on overconsolidated specimens are conducted in fully saturated and undrained conditions. Small cyclic deviatoric stresses are applied in order to investigate more particularly the behavior under a very large number of cycles, during which an unusual pore pressure evolution is observed. To explain this, undrained triaxial creep tests are performed on reconstituted specimens with different values of OCRs under some specified stress states. The evolutions of axial strain, excess pore pressure, stress ratio, stress path, plastic strain rates and stress dilatancy during undrained creep are discussed. The additional undrained creep tests also show that two processes are simultaneously acting in a competitive manner: increase in the pore pressure due to the cyclic loading and decrease in the pore pressure because of creep. Keywords Constitutive relation Cyclic loading, Creep Soft clay Stress dilatancy Triaxial test
1 Introduction Various design rules are proposed to geotechnical engineers to calculate both shaft capacity and base resistance of piles under axial or lateral loads. Most of these rules are calibrated from in situ tests (e.g., cone penetration test,
& Zhen-Yu Yin [email protected]; [email protected] 1
School of Materials Science and Mechanical Engineering, Beijing Technology and Business University, Beijing 100048, China
2
Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
3
3SR Laboratory, Grenoble Alpes University, UMR CNRS 5521, 38000 Grenoble, France
4
Research Institute of Civil Engineering and Mechanics (GeM), Ecole Centrale de Nantes, UMR CNRS 6183, 44300 Nantes, France
pressuremeter test) that allow estimating the static capacity. However, there are more and more situations where geotechnical engineers may have to consider the effects of repeated loads with variable amplitude with time. Wind, waves, and tides are examples of physical phenomena that induce cyclic loadings
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