含软弱夹层斜坡地震动力响应特性的振动台试验研究

SHAKING TABLE TEST FOR SEISMIC RESPONSES OF SLOPES WITH A WEAK INTERLAYER

斜坡中的软弱夹层往往控制着其变形破坏模式。在地震作用下,软弱夹层与地震波的复杂作用机制使得该类斜坡的地震响应特征很难被充分了解。在已有认识的基础上,开展4个含软弱夹层斜坡模型的振动台试验,旨在通过与均质斜坡模型响应进行比较,揭示含软弱夹层斜坡的地震动力响应特性,并观察软弱夹层在这一响应过程中所起的作用。主要研究结果为:(1)4个含软弱夹层模型的水平分量(PHA)和竖直分量(PVA)加速度响应均呈现出高程放大效应,且主要体现在夹层以上部位。在夹层以下部位,水平分量加速度放大系数始终保持在1.5以内。(2)与均质模型响应的比值表明,在夹层以上部位,夹层的存在对2个加速度分量的影响与夹层特征和激振强度密切相关。当激振强度较弱(≤0.3 g)时,厚夹层和薄夹层的存在都能对PHA和PVA响应起到增强作用。当激振作用增强时,厚夹层表现出了隔震作用,在坡顶,PHA和PVA响应相对均质模型分别减弱50%和70%。(3)与加速度响应一致,坡表水平向位移响应也呈现出了高程放大特征,且在坡顶最大。然而,与均质斜坡模型的初始变形出现在坡顶这一现象不同的是,含夹层模型的变形最早出现在夹层以上、坡顶以下的部位。分析产生这一差异的可能原因在于,当激振强度较大时,含夹层模型相对于均质模型在该部位的水平向响应强度显著增强,而夹层的挤压变形也可能造成初始变形部位更靠近夹层。(4)含软弱夹层模型的最终破坏部位和破坏程度,与夹层的厚度和倾角密切相关,表现为含水平夹层模型的破坏部位高于含反倾夹层模型,而含薄夹层模型的破坏程度高于含厚夹层模型。

The weak layer in a slope always controls slope deformation and failure mode. Under an earthquake,the complex interaction mechanism between the weak interlayer and the seismic waves hinders the understanding of the dynamic responses of this type of slope. Based on the existing knowledge,shaking table tests were conducted for four slope models containing a weak interlayer. The effects of the weak interlayer were uncovered by comparing the responses of the models with and without a weak interlayer. Both the horizontal(PHA) and vertical(PHA) acceleration responses were amplified along the altitude for all four slope models,especially in the locations with the elevation higher than the interlayer. In the locations with the elevation lower than the interlayer,the PHA amplification factor remained within 1.5. In comparison with the homogeneous model,the existence of an interlayer resulted the two component responses in the upper part of slope strongly depended on the features of the interlayer and the input intensity. When the input intensity was weak(≤0.3 g),the responses for the models with a thin or a thick interlayer were stronger than in the homogenous model. With the increasing of the input intensity,the thick interlayer generated an effect of seismic isolation,which caused the PHA and PVA responses at the slope crest decreasing by 50% and 70% respectively. The horizontal displacements on the slope surface were amplified and reached the maximum value at the crest. The initial deformation occurred at the top of for the homogeneous model slope. However,for the four models with a weak interlayer,the deformation was firstly observed in the position above the interlayer and below the crest. The location and the degree of the slope failure were closely related to the thickness and the dipping angle of the weak interlayer. The model with a horizontal interlayer caused the failure location higher than the models with an anti-dip interlayer and the model with a thin interlayer caused the failure more severe than the one with a thick interlayer.