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Gold Science and Technology ›› 2023, Vol. 31 ›› Issue (1): 102-112.doi: 10.11872/j.issn.1005-2518.2023.01.101

• Mining Technology and Mine Management • Previous Articles     Next Articles

Research on Meso-mechanical Properties of Rock Under Different Stress Paths Based on Discrete Element Method

Jielin LI1,2(),Jingyao WANG1,Yigai XIAO1,2,Xiaoshuang LI3   

  1. 1.School of Resources and Safety Engineering, Central South University, Changsha 410083, Hunan, China
    2.State Key Laboratory of Safety and Health for Metal Mines, Maanshan 243000, Anhui, China
    3.School of Civil Engineering, Shaoxing University, Shaoxing 312000, Zhejiang, China
  • Received:2022-08-10 Revised:2022-10-19 Online:2023-02-28 Published:2023-03-27

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Abstract:

The stress state of rock mass in engineering has an important influence on the stability of surrounding rock.At present，scholars at home and abroad mainly study the deformation and failure of rock during loading and unloading through rock mechanics tests such as uniaxial compression and conventional triaxial compression.However，in the process of excavation，the stress state of the rock mass in the radial direction is unloaded and the axial direction is loaded，which is more in line with the actual working conditions.Therefore，the results obtained by traditional research methods can’t truly reflect the stress state of rock mass.There are still some limitations to reflect the stress unloading effect and mechanical characteristics of rock excavation in underground engineering by laboratory test.Moreover，due to the differences of test conditions and rock types，the initial damage degree in the process of rock sample processing is different，the load control methods in the test are different and the number of repeated samples is small，which leads to the dispersion error of test results larger than the true range of stress path’s influence on strength.In order to study the influence of stress state on the stability of surrounding rock in rock mass engineering，based on the discrete element theory，the stress state in the process of underground roadway excavation was analyzed，and triaxial compression numerical simulation tests under three different unloading paths，i.e. confining pressure unloading-axial pressure increasing，confining pressure unloading-axial pressure unchanged and confining pressure unloading-axial pressure decreasing，were carried out.Compared with conventional triaxial compression tests，the macroscopic strength characteristics and microscopic damage process differences of rocks under different stress paths were analyzed.The results show that with the increase of confining pressure，the macroscopic crack of rock changes from tensile crack under uniaxial compression to single inclined plane shear crack under low confining pressure，and finally the conjugate crack shape appears under high confining pressure，which indicates that confining pressure is an important factor affecting the crack state of rock.The failure of the same rock under different unloading paths also follows Hoek-Brown strength criterion，that is，different stress paths will not affect the ultimate strength of the rock.The aggregation characteristics of contact force vector projection scatterplots under different unloading paths are similar，so the stress tensor state is not affected by unloading paths，but the damage process is different under different stress paths.Micro-cracks develop most intensively under the stress path of confining pressure and unloading-constant axial pressure.The crack cluster speed is the fastest under the stress path of confining pressure unloading and axial pressure increasing.The research results can provide reference for stress unloading failure analysis of surrounding rock in the process of underground roadway excavation.

Key words: stress path, discrete element, damage process, strength criterion, stress tensor, crack propagation

CLC Number: 

  • TD853

Fig.1

Variation of surrounding rock stress during unloading process of underground roadway"

Fig.2

Four stress path schemes in roadway excavation process"

Fig.3

Conventional triaxial compression test scheme"

Fig.4

Unloading stress path test scheme"

Table 1

Meso-parameter value of discrete element"

参数名称数值参数名称数值
模型宽度/mm50颗粒刚度比1.5
模型高度/mm100颗粒阻尼系数0.5
颗粒半径/mm1.00~1.66拉伸强度/MPa30
密度/（kg·m-3）2 500内聚力/MPa30
孔隙度0.1黏结摩擦角/（°）30
摩擦系数0.5黏结有效模量/GPa13.0
有效模量/GPa13.0黏结刚度比6.0

Fig.5

Calibration results of sandstone samples under 20 MPa confining pressure"

Fig.6

Macrocracks of conventional triaxial discrete element test"

Fig.7

Stress-strain curves of conventional triaxial discrete element test"

Fig.8

Fitting results of GHB criterion"

Fig.9

Displacement，stress and crack propagation under confining pressure unloading-axial pressure constant stress path"

Fig.10

Displacement，stress and crack propagation under confining pressure unloading-axial pressure increasing stress path"

Fig.11

Displacement，stress and crack propagation under confining pressure unloading-axial compression reduction stress path"

Fig.12

Vector scatter plot of normal contact force"

Fig.13

Vector scatter plot of tangential contact force"

Fig.14

Distribution of of cracks number and cracks inclination angle"

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