The ancient landslides development characteristics and stability evaluation along the Luding Section, Dadu River, western Sichuan Province
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摘要:
川西大渡河泸定段地形地貌和地质构造复杂，地质灾害特别是古滑坡极发育。通过遥感解译、InSAR形变分析、野外调查等手段，在泸定县城上游约25 km（至姑咱镇）到下游约43 km（至得妥镇）段发现229处崩塌、滑坡、泥石流等地质灾害，古滑坡规模大、部分具有复活迹象。地质时代测年数据表明，该区古滑坡主要发育于120 ka左右、25~10 ka和全新世3个周期段，与大渡河断裂带活动性密切相关。以泸定县大坪上古滑坡为例，通过ANSYS软件，开展天然状态（自重）和暴雨状态下滑坡的稳定性分析。结果表明，该滑坡在天然状态（自重）和暴雨状态下稳定系数分别为1.2和1.15，暴雨情况下的稳定系数比自重情况下低，并且在暴雨作用下滑坡中下部变形趋势明显加大，有沿边坡临空面滑移的趋势，滑面主要位于陡坡中等风化层中，而天然状态下仅在坡体中部松散堆积层及中等风化层上部形成潜在滑动面。古滑坡的发育特征与稳定性严重影响铁路、公路、水电站等重大工程规划建设，应加强古滑坡的识别、成因机理分析与稳定性评价。
Abstract:The topography and geological structure are very complex along the Luding section of Dadu River, western Sichuan Province. The geological hazards, especially ancient landslides are extremely developed in this area. By means of remote sensing interpretation, InSAR deformation analysis and field investigation, 229 collapses, landslides and mudslides were discovered in the section from about 25 km upstream(to Guzan Town) to about 43 km downstream(to Detuo Town) of the Luding County. In addition, the ancient landslides in this area are large in scale, and some of them have signs of revival. The geological dating data show that the ancient landslides in this area were mainly developed in three periods around 120 ka, 25~10 ka and Holocene, and closely related to the activity of the Dadu River fault. The Dapingshang ancient landslide in Luding County was taken as a study case to analyze the stability of the landslide in natural state (self weight) and heavy rainfall state through ANSYS software. The results show that the stability coefficient of the landslide in natural state (self weight) and heavy rainfall state is 1.2 and 1.15 respectively. The stability coefficient under heavy rainfall conditions is lower than that under self-weight conditions; the deformation of the middle and lower part of the landslide tends to increase obviously under the action of heavy rainfall, and there is a tendency to slip along the empty surface of the slope. The slip surface is mainly developed in the medium weathered layer of the steep slope, but in the natural state, the potential slip surface is only formed in the loose accumulation layer in the middle of the slope and the upper part of the medium weathered layer. The developmental characteristics and stability of ancient landslides seriously affect the planning and construction of railway, highway, and hydroelectric power station projects. Therefore, it should be suggested to strengthen the identification, mechanism analysis and stability evaluation of ancient landslides.
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Key words:
- western Sichuan /
- Dadu River /
- ancient landslide /
- stability /
- numerical simulation
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表 1 大渡河流域典型古滑坡形成时间与大渡河断裂分布关系
Table 1. Relationship between the formation time of typical landslides and the Dadu River faults in the Dadu River basin
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表 2 数值模拟主要岩土体力学参数
Table 2. Modeled mechanical parameters of rocks and soil
岩组编号 岩性 容重/(kN·m-3) 体积模量K/MPa 剪切模量G/MPa 粘聚力c/kPa 内摩擦角φ/° 泊松比μ 1 残坡积物 2100 800 1450 48 36 0.35 2 强风化闪长岩 1870 1100 650 50 40 0.3 3 断裂带 2100 1500 950 100 45 0.32 7 中风化闪长岩 2600 4100 2100 350 45 0.20 8 微-未风化闪长岩 2750 5000 2600 500 45 0.18
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