不同地质条件下边坡动力特征的DDA方法分析

为了对边坡动力响应特征进行分析,基于非连续变形分析(DDA)方法,改进了部分程序,并利用改进的DDA建立了边坡分析模型。该模型绘制了坡体中加速度放大系数等值线图,首先验证了模型黏滞边界的远近对边坡动力响应特征影响极小;其次,分析了不同坡角、坡高、岩性及输入一定地震波周期条件下的边坡加速度放大系数等值线随高程及水平深度的变化特征。分析表明:坡角、坡高小于一定值时,加速度放大系数随高程及水平深度增加呈递增趋势,同一边坡岩性较硬或输入波周期较长时,加速度放大系数较大;而当边坡中存在节理及软弱夹层等不利地质体时,地震波传播会受到反射和透射作用的影响,从而影响边坡的动力特征。经DDA模拟计算揭示:当岩体弹性模量较大时,节理对地震波传播的透射作用较强,且当节理间距与输入波长的比值小于临界值时,其比值越大,节理对波的透射作用越强;岩体分界面下部岩性较上部岩性硬时,随着2种岩体弹性模量差值增大,透射波峰值加速度衰减越明显,而反之分界面以下岩体较上部软时,随2种岩体弹性模量差值增大,透射波峰值加速度放大越明显;当软弱夹层厚度以及其与周围岩体波阻抗的比值较大时,地震波经过软弱夹层时的透射作用较小。

Discontinuous Deformation Analysis of Slope Dynamic Characteristics under Different Geological Conditions

In order to analyze the dynamic response of slope, we establish a slope analysis model by using improved DDA(discontinuous deformation analysis), and obtain contours of acceleration amplification coefficient in slope body. First of all, we verify that viscous boundary distance has minimal effect on dynamic response characteristics of slope. Secondly, we analyze the changes of amplification coefficient with elevation and depth in the presence of different slope angles, slope heights, lithology, periods of seismic wave, etc. Analysis shows that, 1) if slope angle or slope height is smaller than a certain value, amplification coefficient increases with elevation and depth; 2) harder rock or longer period of input wave will lead to bigger amplification coefficient; 3) in case of adverse geological bodies such as joint and weak interlayer, seismic wave propagation will be influenced by reflection and transmission, thus affecting dynamic response characteristics of slope. On the basis of DDA, we can find the following results. Big elastic modulus is in favor of transmission effect of joint on wave propagation. When the ratio of joint spacing to input wave length is smaller than critical value, the greater the ratio is, the stronger the effect of joint on transmission wave is. If rock under interface is harder than that above the interface, and when the difference between two elastic modulus increases, the reduction of peak acceleration in transmission wave gradually tends to be obvious. On the contrary, the reduction will be changed into amplification. When weak interlayer thickness or ratio of the thickness to acoustic impedance in surrounding rock is bigger, transmission effect of seismic wave through weak interlayer is smaller.