CHARACTERISTICS AND DEFORMATION MECHANISM OF SHUIWAN SEISMIC LOESS LANDSLIDE IN MAIJI, TIANSHUI
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摘要: 以天水市税湾地震黄土滑坡为例, 依据野外调查和室内测试结果, 总结天水地区历史地震黄土滑坡特点, 剖析地震黄土滑坡发生的力学机制, 初步提出历史地震黄土滑坡的识别标志。税湾滑坡及柳沟右岸滑坡群属典型的地震黄土滑坡, 具有规模大、滑动面切割深、滑坡坡度小、成群成带分布和高位下滑等特点, 可作为识别历史地震黄土滑坡的重要标志。税湾滑坡及柳沟右岸滑坡群坡体具有明显的黄土/泥岩二元斜坡结构, 极易沿黄土/泥岩接触面滑动。当坡体受到地震力作用时, 地震产生的循环动荷载一方面降低滑坡岩土体的抗剪强度, 另一方面改变滑坡体的力学状态, 坡体应力平衡遭到破坏, 地震力增加坡体下滑力、减小坡体抗滑力, 导致坡体失稳发生滑坡。目前, 税湾滑坡处于欠稳定状态, 遇地震或强降雨有可能再次失稳下滑, 因而有必要进一步开展地震黄土滑坡的成灾模式研究, 为潜在强震区防灾减灾提供科学依据。Abstract: Many historical earthquakes happened in Tianshui and its adjacent region, which resulted in seismic loess landslides developing extremely. According to field survey and indoor synthetic analysis, Shuiwan landslide and landslide groups of Liugou belong to typical seismic loess landslides, which are usually performance for large-scale, the sliding surface cutting deeply, thickness greatly, small slope, distributed along zones, appeared in groups and decline in high position and other characteristics. The characteristics above can be used as important symbols of field identification of seismic loess landslides. The slopes involved in Shuiwan landslide and the right bank Liugou landslides are characterized by loess/mudstone slope double layers structure. Under the condition of internal power, it is easy to slip along the loess/mudstone contact surfaces. Under the dynamic circulative loading, shear strength of the landslide rock mass is decreased on one hand. On the other hand it also changes the mechanical status of landslide, and the balance of the slope body is destroyed, which induce landslide happened. So, Shuiwan landslide is still in understable state. In case of an earthquake or heavy rainfall, it is likely to reoccur again. There is a necessary for further research of the disaster model of seismic loess landslide. It will provide a scientific basis for prevention and mitigation disaster of potential meizoseismal area.
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图 1 天水地区主要活动断裂及地震分布图(据文献[14]修编)
Figure 1. The main active faults and earthquakes distribution in Tianshui area
表 1 柳沟冲沟两岸滑坡特征统计
Table 1. Characteristics statistics of landslides in both sides of Liugou
滑坡位置 滑坡编号 长×宽(m) 厚度/m 规模/(104 m3) 切割深度/m 距梁顶水平距离/m 坡度/(°) 滑坡成因类型 柳沟右岸 1 500×600 40~50 750 20~30 0 13 地震 2 200×100 10~15 12 6~10 0 10 地震 3 600×350 80 800 40~50 0 12.5 地震 4 550×450 80~100 990 50~60 0 13 地震 5 500×400 80~100 800 70~80 0 15 地震 柳沟左岸 6 250×400 20 150 0~5 300 15 降雨 7 800×500 30 700 20~30 150 12 地震 8 100×100 20 10 0 120 40 降雨 9 200×200 40 100 0 80 35 降雨 10 150×100 10~20 15 0 80 32 降雨 11 180×150 15 16 0 50 28 降雨 12 200×150 10~15 30 0 30 35 降雨 13 230×190 30~40 80 0 50 40 降雨 表 2 滑床岩土体部分物理力学性质表
Table 2. Physical and mechanical properties of rock and soil mass of slider bed
岩土体类型 密度/(g·cm-3) 含水率/% 渗透系数/(10-6 cm·s-1) 粘聚力/kPa 内摩擦角/(°) Q3黄土 1.88~1.92 18.0~19.0 5~20 30.2~49.4 23.7~29.2 古土壤 2.01~2.06 18.1~22.0 0.4~1.2 48.0~85.6 25.0~32.9 风化带土 1.98~2.02 20.6~24.2 40~60 34.2~54.0 22.2~28.5 泥岩 2.03~2.12 15.9~24.1 0.01~0.10 117.0~193.0 21.8~32.0 -
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