Evolution law of open fracture of coal body and instability precursor test
WANG Lei
LIU Huaqiang
LI Shaobo
ZHANG Yu
LIU Huaiqian
CHEN Lipeng
WANG Ancheng
Abstract：In order to explore the precursor information of coal instability with different fracture distribution characteristic parameters,uniaxial loading test was carried out based on MTS 816 test system,the mechanical characteristics and fracture evolution law of coal body were analyzed,the accurate expression of crack initiation angle was derived,and the mechanical model of bending crack was established.The results show that the deterioration of the coal body increases with decreasing crack azimuth,but the strength is lower than that of the intact specimen,and the length of the cracks is negatively correlated with the strength of the specimen.The shear interlocking effect makes the stress-strain curve of fractured coal body show a double hump shape.The interlocking strength is negatively correlated with the azimuth angle,but has no obvious correlation with the length.The characteristic parameters of fracture distribution play a significant leading role in the formation of local high strain zone in the initial strain field.When the azimuth angle is between 0° and 90°,the spatial deduction forms of strain concentration,dispersion and fracture propagation are highly unified.The dynamic shear factor(τ0)of the crack end is defined and its expression is obtained.The type Ⅱ SIF is im-proved and the exact crack initiation angle expression is derived.It is concluded that the crack initiation angle is negatively correlated with the azimuth angle.Comparing the disturbance coef-ficient e(KⅡ/KⅠ)before and after shear interlocking,it can be seen that the shear interloc-king effect can cause type Ⅱ failure by inhibiting the wing-like type Ⅰ expansion at the crack tip,and the inhibition effect is negatively correlated with the azimuth angle.Compared with surface strain monitoring,the variation characteristics of interlocking strength can provide more positive precursor information for the sudden failure of coal under different fracture dis-tribution characteristic parameters.
Keywords：open crackDIC monitoringshear interlocking strengthend shear dynamic fac-torequivalent crack model
Publication Date：2024-03-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：14( 250-263 )