青藏高原东南三江流域黄土类堆积体斜坡地震作用下的动力响应试验研究——以四川巴塘下归洼滑坡为例

Experimental study on the dynamic response of accumulation slopes under earthquake action in Three-rivers Basin, southeast Tibetan Plateau: a case study of the Xiaguiwa landslide in Batang, Sichuan Province

摘要:

青藏高原东南三江流域广泛存在堆积体斜坡,该类斜坡极易演化为滑坡灾害。以四川巴塘下归洼斜坡为例,通过振动台模型试验研究地震诱发的堆积体滑坡动力响应特征与破坏模式。试验结果表明,在地震作用初期,由于孔隙被挤密,斜坡的自振频率增大；在茂县波激励下,斜坡肩部动力响应最强烈。高幅值茂县波激励下,因斜坡整体刚度降低,放大效应减弱。Hibert谱描述了地震波在斜坡中的传播特征,向斜坡顶部传播时,地震波高频能量显著增强,地震波经过堆积层后,放大效应减弱。在足以致使堆积层滑动的强震作用下,坡表一定深度下动力响应呈现一致剧烈现象,斜坡上部会形成“脱离体”,“脱离体”在地震作用下上下颠簸运动;在临滑时,坡表出现最强烈的动力响应。斜坡的破坏模式为:地震初期,在重力和地震耦合作用下,坡表土体剥落;随地震幅值增加,坡肩与堆积层发生明显相对位移,堆积层表面出现裂缝;最终,坡脚发生明显相对位移,随后堆积层偏离基岩加速滑塌。基于地震信号特征的斜坡堆积层滑落过程可分为三阶段:(1)稳定阶段;(2)临滑阶段;(3)滑移阶段。

Abstract:

The three-river basin of the southeast Qinghai—Tibet Plateau has widespread accumulation slopes, which can easily evolve into landslide disasters. In this study, the dynamic response characteristics and failure modes of earthquake-induced accumulation landslides in the Xiaguiwa slope in Batang, Sichuan Province, were investigated with shaking table model tests. Results show that the natural frequency of the slope increases because of the compaction of pores in the early stage of earthquake action. Under the excitation of a Maoxian wave, the slope shoulder responds strongly. Under the excitation of a high-amplitude Maoxian wave, the amplification effect weakens because of the decrease in the overall stiffness of the slope. The Hibert spectrum describes the propagation characteristics of the seismic wave in the slope. When propagating to the slope top, the high-frequency energy of the seismic wave is considerably enhanced. The amplification effect weakens after the seismic wave passes through the accumulation layer. Under the action of strong earthquakes, the response of the slope surface at a certain depth shows a consistent and violent phenomenon. The upper part of the slope will form a “detachment body”, which will show upward and downward jerky motion under earthquake action. The strongest dynamic response appears at the slope surface approaching a slip. The characteristics of the failure mode of the slope are as follows: in the early stage of the earthquake, soil peeling occurs on the slope surface under the coupled action of gravity and earthquake; as the earthquake amplitude increases, relative displacement occurs between the slope shoulder and the accumulation layer, and cracks appear on the surface of the accumulation layer; finally, obvious relative displacement occurs at the slope toe, and the accumulation layer deviates from the bedrock and accelerates to collapse. The sliding process of the slope accumulation layer can be divided into three stages according to the characteristics of seismic signals: (1) stable stage, (2) impending slip stage, and (3) slip stage.