基于DDA方法的不利地质结构对弹性纵波传播规律的影响研究

Effect Research of Unfavorable Geologic Structure on Elastic P-wave Propagation Using DDA Method

基于黏性边界理论,在DDA程序中实现了适用于底部输入地震波的人工边界条件,并通过算例验证了其合理性。采用改进的DDA方法研究了节理的刚度和间距、软弱夹层的厚度和波阻抗对弹性纵波传播规律的影响。计算结果表明:节理面透射系数的理论解与DDA数值解差别较小;随着法向刚度的降低,节理对弹性纵波的衰减作用增大;节理间距存在门槛值和临界值,在不同的取值范围,对弹性纵波的衰减规律不同;弹性纵波在分界面上的透射系数的理论解和DDA数值解基本一致;软弱夹层厚度影响多重透射波的干涉效应,厚度越小,干涉效应越强;随着软弱夹层与周围岩石的波阻抗比值的降低,软弱夹层对地震波的衰减作用越来越明显。

Based on viscous boundary theory,the artificial boundary was implemented in DDA method and well proved with a specific example.Using the modified DDA method,the influence of joint stiffness,joint spacing,weak intercalation thickness,and impedance on elastic P-wave propagation were studied.The results showed that,the difference of transmission coefficient of joint surface between DDA calculation and theoretical solution is very small.The attenuation of elastic P-wave increases with the decrease of joint stiffness.There exists threshold value and critical value for joint space.In different ranges,the wave attenuation law is different.The transmission coefficient of elastic P-wave on interface calculated by DDA method is very close to the theoretical solution.Weak intercalation thickness affects the interference effect of multiple transmission.The attenuation of elastic P-wave increases with the decrease of weak intercalation impedance.