Fractional-order creep model for soft clay under true triaxial stress conditions
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ORIGINAL PAPER
Fractional-order creep model for soft clay under true triaxial stress conditions Liu Jiashun 1,2,3 & Jing Hongwen 2 & Meng Bo 2 & Wang Laigui 3 & Yang Jianjun 1 & You Yanwei 1 & Zhang Sijin 1 Received: 3 September 2019 / Accepted: 12 August 2020 # Saudi Society for Geosciences 2020
Abstract To investigate the creep characteristics of soft clay under true triaxial stress conditions, multistage loading creep tests using TSW40 true triaxial apparatus were performed. The creep deformation characteristics, creep rate, and long-term strength of soft clay under a true triaxial stress path were studied. The results showed that the creep deformation and creep rate of soft clay increase with increasing major principal stress; the axial deformation is larger than the lateral deformation. The long-term strength and the equation for predicting the starting point of accelerated creep were obtained using the generalized shear stress. A four-element fractional-order creep (FFC) model based on the fractional Burgers creep model was established for soft clay and then extended to three dimensions. The model calculation results based on the parameters obtained using MATLAB’s Curve Fitting Toolbox were in good agreement with the experimental results. The comparison results showed that the 3D FFC model was more accurate at describing the entire creep curve of soft clay than the fractional Burgers model and the Burgers model, particularly regarding the accelerated creep characteristics. In conclusion, the results presented herein are expected to provide the scientific basis for determining soft clay creep instability under true triaxial stress conditions. Keywords Soil mechanics . Soft clay . True triaxial stress test . Burgers model . Fractional-order model . Creep deformation
Introduction Soft clay presents unique rheological properties that can easily cause foundation instability, landslides, or other geotechnical problems. Therefore, research on the creep characteristics of soft soil is very important to ensure the safety of the engineering. However, most previous geomaterial research is based on conventional triaxial stress conditions, whereas the majority of soils in practical engineering applications experience complex triaxial stress conditions; thus, their mechanical Responsible Editor: Zeynal Abiddin Erguler * Liu Jiashun [email protected] 1
College of Civil Engineering, Liaoning Technical University, Fuxin 123000, China
2
State Key Laboratory for Geomechanics and Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221116, China
3
School of Mechanics and Engineering, Liaoning Technical University, Fuxin 123000, China
characteristics and failure behaviors differ significantly from those in the 1D or 3D stress states (Isakhanov 2000; Liu and Shao 2018). So far, many true triaxial tests were performed to investigate the influence of intermediate principal stress on the stress–strain and strength behavior of clays and sands (Shao and Luo 2011; Shi et al. 2011). An empirical equa
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