Creep Characteristics and Constitutive Model of Gneiss in Zilashan Area Along Sichuan-Tibet Railway Line

doi:10.19657/j.geoscience.1000-8527.2021.008

Abstract

Abstract:

Gneiss is widely distributed in the Zilashan area along Sichuan-Tibet railway line, and the anisotropic characteristics of the rocks are remarkable. During the construction of deep-buried tunnels, wallrock deformation directly affects the stability and reinforcement measures. To reveal the creep characteristics of gneiss from the Zilashan area in western Sichuan to eastern Tibet, triaxial compression creeping tests were carried out. Therefore, an abnormal crack propagation phenomenon was discovered. Based on the superposition principle, the long-term strength was determined by drawing an isochronous stress-strain curve. Using the Burgers model, a creep constitutive model that is more suitable for engineering practice was established. The parameters were then identified through L-M algorithm and global optimization. The results clearly show that under the same confining pressure condition, instantaneous strain increment of the samples decreases with increasing stress level, and consequently hardening occurred. From the sample creep characteristics, the phenomenon of abnormal crack propagation caused by microstructure anisotropy occurs, and the sample creep rate increases sharply due to abnormal crack propagation in the attenuation creep stage. The long-term strength increases with peristaltic pressure. Compared with the conventional triaxial test, the long-term strength decreases by 59.8% and 21.3%, respectively, and the improved Burgers model is more practical. The mechanical testing parameters can form a scientific basis for engineering construction and disaster prevention and control.

Key words: Sichuan-Tibet railway, gneiss, triaxial compression creep test, abnormal crack propagation, constitutive model

CLC Number:

P642
TU45

WANG Lei, GUO Changbao, GUO Pengyu, JI Feng. Creep Characteristics and Constitutive Model of Gneiss in Zilashan Area Along Sichuan-Tibet Railway Line[J]. Geoscience, 2021, 35(01): 153-160.

Figures/Tables 11

Fig.1 Schematic diagram of the grading loading creep test

Fig.2 Curves showing the relation of axial strain vs. time for samples

Fig.3 Curves showing the relation of instantaneous strain increment vs. axial stress of samples

Fig.4 Schematic diagrams of step creep of group A samples

Fig.5 Curves of creep rate of samples

Fig.6 Curves showing the relation of axial isochronous stress vs. strain of samples

Fig.7 Nonlinear sticky kettle element

Fig.8 Burgers mechanical model

Fig.9 Improved Burgers mechanical model

Fig.10 Comparison between the calculated results using the improved Burgers model and the experimental results

Table 1 Parameters of the improved Burgers model

$σ 3$ / MPa	$σ 1$ / MPa	$K$ / GPa	$G 1$ / GPa	$η 1$ / (GPa·h)	$G 2$ / GPa	$η 2$ / (GPa·h)	$η nl$ / (GPa·h)	R²
5	28.6	5.63	3.38	7.41×10⁷	200.46	170.14		0.98
5	57.1	6.02	3.61	1.09×10⁶	216.34	437.90		0.90
5	85.7	6.51	3.90	1.76×10⁷	9.01×10³	6.73×10³		0.92
10	30.6	2.08	1.25	9.62×10⁷	19.04	129.27		0.98
10	61.2	2.06	3.44	9.32×10⁶	341.66	49.97		0.91
10	91.8	2.64	4.40	3.89×10⁵	557.75	308.12		0.96
10	122.5	3.33	5.54	3.04×10⁴	545.45	420.09		0.91
10	153.1	3.31	5.52	1.08×10⁶	5.24×10⁴	2.08×10⁵	4.45×10⁶	0.95

Table 1 Parameters of the improved Burgers model

$σ 3$ / MPa	$σ 1$ / MPa	$K$ / GPa	$G 1$ / GPa	$η 1$ / (GPa·h)	$G 2$ / GPa	$η 2$ / (GPa·h)	$η nl$ / (GPa·h)	R²
5	28.6	5.63	3.38	7.41×10⁷	200.46	170.14		0.98
5	57.1	6.02	3.61	1.09×10⁶	216.34	437.90		0.90
5	85.7	6.51	3.90	1.76×10⁷	9.01×10³	6.73×10³		0.92
10	30.6	2.08	1.25	9.62×10⁷	19.04	129.27		0.98
10	61.2	2.06	3.44	9.32×10⁶	341.66	49.97		0.91
10	91.8	2.64	4.40	3.89×10⁵	557.75	308.12		0.96
10	122.5	3.33	5.54	3.04×10⁴	545.45	420.09		0.91
10	153.1	3.31	5.52	1.08×10⁶	5.24×10⁴	2.08×10⁵	4.45×10⁶	0.95

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