Unsteady fractional stress relaxation time effect model
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ORIGINAL PAPER
Unsteady fractional stress relaxation time effect model Shuguang Zhang 1,2 & Lei Chen 3 & Wenbo Liu 1 Received: 16 May 2020 / Accepted: 1 November 2020 / Published online: 11 November 2020 # Saudi Society for Geosciences 2020
Abstract The study of rock stress relaxation characteristics is an important aspect of the research of its long-term mechanical characteristics. It is also the key to ensure the long-term safety and stability of the surrounding rock of the high-ground-stress roadway. Using the MTS815.02 triaxial test system, the stress relaxation test of the sandstone of Fuxin Hengda Coal Mine with a confining pressure of 30 MPa is carried out. A new unsteady fractional stress relaxation aging constitutive model is established by constructing the relationship between damage variables, time, and model parameters and considering that the fractional order is affected by the time effect. The correctness and rationality of the model are verified by experimental data. Test results show that as the relaxation damage develops during relaxation, the relaxation has evident nonlinear characteristics. The model curve is highly consistent with the experimental curve, which indicates that the unsteady model is suitable for reflecting the deformation of rock stress relaxation. It can better describe the whole process of stress relaxation change. This study can provide a scientific basis for the long-term stability analysis of Fuxin Hengda high in situ stress sandstone roadway. Keywords Long-term stability . Stress relaxation . Unsteady fractional order . Confining pressure . Damage variable . Sandstone . Roadway
Introduction The maximum buried depth of the sandstone roadways taken is approximately 800 m. The in situ stress in the excavated area reaches 30–40 MPa, which is a typical high in situ softrock tunnel (Sun and Hu 1997; Hao et al. 2012). In excavating high-ground-stress roadways, the long-term mechanical properties of the surrounding rock of the roadway must be accurately grasped to ensure the construction safety and long-term stability of the roadway (Haupt 1991; Pend and Podneiks 1972; Lodus 1986). The long-term mechanical properties of the surrounding rock of the roadway include two important aspects: creep Responsible Editor: Zeynal Abiddin Erguler * Wenbo Liu [email protected] 1
Guangxi Key Laboratory of Geomechanics and Geotechnical Engineering, Guilin University of Technology, Guilin 541004, Guangxi, China
2
School of Civil Engineering, Guilin University of Technology, Guilin 541006, Guangxi, China
3
School of Civil Engineering, Liaoning Technical University, Fuxin 123000, Liaoning, China
and relaxation (Zhang and Liu 2019; Liu and Zhang 2020). Creep is the gradual increase in the deformation of geotechnical materials with time under constant load. Relaxation is the gradual decrease of the stress of geotechnical materials with time under constant strain. For high-ground-stress roadways, the initial support before the secondary lining construction is flexible support; the surrounding r
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