基于振动台模型试验的二元结构边坡地震动力响应研究

SEISMIC RESPONSE OF DUAL STRUCTURE SLOPE BASED ON SHAKING TABLE MODEL TEST

在强震区,地震诱发边坡失稳等地质灾害的安全隐患十分突出。同时,针对由上覆松散堆积物和下卧基岩构成的土岩二元结构边坡,其地震作用下动力响应的相关研究仍较为少见。因此本文以海西福永高速ZK132+300段典型土岩二元结构边坡为原型,设计制作了1/20缩尺模型边坡,在福建省土木工程灾害防治重点实验室的双向地震模拟振动台上,完成了20种工况的模拟地震动试验。重点关注坡体高程、地震动幅值、地震动频率特征对PGA放大系数的影响,得到以下结论。坡内和坡面各测点处PGA放大系数,均呈现出明显的高程效应和鞭梢效应;但锚框支护能有效抑制坡面的趋表效应。随着输入地震动幅值的增大,土体表现出明显的塑性特征,坡内和坡面各测点处PGA放大系数,按高程依次呈线性减小或指数型减小。在相同幅值、不同频率特征的地震波作用下,坡面各测点处PGA放大系数呈现出明显的差异性;但这种因地震波频谱特性不同而产生的差异,随着高程增加而逐渐减小,并在坡顶处趋向一致。同时通过对边坡表观破坏特征的描述,发现二元结构边坡的裂缝发展仅出现在上部土质坡体的坡顶和坡肩自由面附近,未出现贯通性裂缝和整体滑移失稳,认为锚框支护结构极大提高了上部土质边坡的抗震性能。

Geological disasters such as slope failure,caused by earthquake,are very common in meizoseismal area. The dual structure slope is composed of underlying rock mass and overlying soil mass. The seismic responses of dual structure slope with anchor- frame reinforcement remain unclear. Based on the prototype slope with dual structure at the ZK132＋300 of Fuyong Expressway,a 1 / 20 downscale model slope is designed and built. Shaking table tests with 20 loading cases are then conducted in the key laboratory of disaster prevention of Fujian Province.The influences of slope elevation,seismic wave amplitude and seismic wave spectrum on the PGA amplification coefficients are focused in this article. Some conclusions can be drawn as follows. The PGA amplification coefficients inside and upon the slope increase with the slope elevation and magnify dramatically at the top of slope.The anchor- frame support restrains the PGA amplification coefficients upon the slope,comparing with their counterparts inside the slope. Due to the plasticity of soil,the PGA amplification coefficients decease linearly or exponentially with the seismic wave amplitude. Excited by the seismic waves with same amplitude and different spectrums,there exists some difference among the PGA amplification coefficients upon the slope. However,the distinction due to seismic wave spectrum fades away with the slope elevation and vanishes at the top of slope. The failure characteristic of model slope during shaking table tests is carefully inspected and described. The cracks only occur near the free face of slope top and slope shoulder,and no interconnected crack and overall instability occur during tests. It is concluded that the anchor-frame reinforcement can improve the seismic performance of soil slope significantly.