Study On Dynamic Fragmentation Distribution Of Rock Considering Internal Structure

The internal structure of rocks is very complex,containing numerous irregular micro-cracks,pores,joints,and faults that significantly affect the mechanical properties of rocks.First,this article studies the influence of different joint plane dip angles on the failure mode and fragmentation characteristics of rocks and obtains the compressive strength and static fragmentation characteristics under different joint plane dip angles.Secondly,based on the self-similarity and hierarchy of the internal crack distribution of rocks,a multi-scale crack propagation model is used to study the coalescence behavior of wing cracks under dynamic loads.The instability analysis of the columns formed after the crack propagation is carried out using the dynamic buckling instability model,taking into account the influence of the interaction of cracks of different levels.Using the numerical calculation methods,the equation of dynamic crack propagation and the dynamic loading history are jointly solved to obtain the initiation and coalescence times of cracks of different levels.Finally,the distribution of multi-level cracks is further studied and the influence of the geometry shape of the column after the crack coalescence on the dynamic failure is considered.The dynamic strength and average fragment size under different initial crack densities and strain rates are obtained.The research results are summarized as follows:(1)The influence of joint plane dip angle on the static mechanical properties of rocks was obtained.The experimental results show that as the dip angle of the joint plane increases,the compressive strength decreases first and then increases.The compressive strength is the lowest when the joint plane dip angle is around 60°.The curve of the cumulative mass percentage of fragments under different joint plane dip angles is obtained.The steeper the curve,the lower the degree of fragmentation.It is calculated that the average fragment size increases with the increase of the joint plane dip angle,and the relationship between the average fragment size and the compressive strength is fitted.(2)The influence of strain rate and initial crack density on the dynamic behavior of single-scale and two-scale interaction cracks is revealed.The strain rate and initial crack density have a significant impact on the distribution of dynamic strength and average fragment size.The dynamic strength has a significant rate-dependence.As the strain rate increases,the average fragment size gradually decreases.Large-scale cracks dominate and have a significant inhibitory effect on small-scale cracks.When the interaction of two-scale cracks is considered,the dynamic strength is lower than that of single-scale cracks.With the increase of initial crack density,the dynamic strength decreases,and the average fragment size decreases accordingly.When the initial crack density is high,the impact of changing the initial crack density on the dynamic strength decreases.(3)The effects of initial crack density and strain rate on the initiation and coalescence of multi-scale cracks are clarified,and the effect of the geometric shape of the column after crack coalescence on the dynamic failure was clarified.The calculation results of the multi-scale crack model show that as the initial crack density and strain rate increase,the initiation and coalescence time gradually decrease.As the increase of crack levels(the size decreases),the initiation time gradually increases,while the coalescence time decreases first and then increases.The geometric shape of the column after crack coalescence has a significant influence on the dynamic failure.The analysis shows that with the increase of strain rate,smaller scale cracks are activated,and the average fragment size shows a decreasing trend,which is also the internal mechanism of the decrease of rock fragmentation with the increase of strain rate.