Formation mechanism and stability analysis of a landslide in altered ophiolite in the upper reaches of Jinsha River: A case study of the Duirongtong landslide
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摘要:
青藏高原构造缝合带具有复杂的岩体结构和特殊的岩性组合，是特大滑坡易发带，但蚀变蛇绿岩型滑坡形成演化涉及的影响因素较多，目前对其孕生机制尚不明晰，制约了灾害隐患有效判识和风险防范。以金沙江构造缝合带堆绒通滑坡为例，基于现场调查、无人机测绘、年代学测试和环剪试验等方法，剖析了蚀变蛇绿岩型滑坡的发育特征和形成机制，并对滑坡堆积体的稳定性进行了模拟分析。结果表明：堆绒通滑坡是形成于晚更新世的巨型滑坡，所在斜坡岩性以基性−超基性岩为主，内部发育多条黏土化蚀变蛇绿岩条带，构成易滑地质结构；黏土化蚀变蛇绿岩在天然状态下具有较低的抗剪强度，遇水强度急剧下降，天然状态下的黏聚力（c）、内摩擦角（φ）值分别为67.0 kPa和20.3°，饱和状态下的c、φ值分别为39.8 kPa和13.8°，软化效应显著；堆绒通滑坡堆积体目前整体稳定，但在强降雨条件下滑坡体前缘可能出现局部失稳，基于滑坡稳定性数值模拟结果提出了灾害风险防范对策。综合分析认为，岩体结构与黏土化蚀变岩联合控制了堆绒通滑坡的形成演化。相关认识对青藏高原构造缝合带斜坡稳定性分析和防灾减灾具有较好的启示意义。
Abstract:Objective The tectonic suture zone of the Qinghai-Tibet Plateau has a complex rock mass structure and special lithology combination and is thus prone for large landslides. However, many factors influence the formation and evolution of landslides in altered ophiolite. Their formation mechanism is not clear at present, which restricts an effective identification and disaster risk prevention.
Methods Taking the Duirongtong (DRT) landslide in the Jinsha River tectonic suture zone as an example, field investigations, UAV mapping, geochronological analysis, ring-shear testing, and numerical simulation were performed to analyze the formation mechanisms of the landslide and evaluate the stability of the landslide deposits.
Results The results show that: (1) The DRT landslide is a giant landslide formed in the late Pleistocene. The slope is mainly composed of basic-ultrabasic rocks, and several clay-altered ophiolitic bands are developed, forming a sliding-prone geo-structure. (2) The clay-altered ophiolite has low shear strength under natural conditions, and its shear strength drops sharply when exposed to water. The natural values of c and φ are 67.0 kPa and 20.3°, and the water-saturated values of cohesion(c) and angle of internal friction(φ) are 39.8 kPa and 13.83°. The DRT landslide is currently stable as a whole, but the leading edge of the landslide may experience movement under heavy rainfall. Based on numerical simulation, some preventive recommendations are proposed.
Conclusion The study suggests that the formation and evolution of the DRT landslide are controlled by the combination of geological structure and clay-altered rock. [Significance] These findings have important implications for the slope stability analysis and disaster prevention in the tectonic suture zone of the Qinghai-Tibet Plateau.
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Key words:
- tectonic suture zone /
- landslip /
- ophiolites /
- clay-altered rock /
- sliding-prone geo-structure /
- stability analysis
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表 1 光释光样品年龄测定结果
Table 1. Results of OSL age determination
样品号 埋深/m U/×10−6 Th/×10−6 K/% 等效剂量De(Gy) 年剂量Gy/ka 含水量/% 年龄/ka DRT-01 0.5 1.58 6.69 2.40 254.04±8.03 3.45±0.16 7±5 73.7±4.2 DRT-02 0.5 1.05 9.95 1.55 281.41±1.31 2.75±0.12 7±5 102.4±4.6 
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表 2 黏土化蚀变岩物质组成与滑带土粒度分析
Table 2. Material composition of clay-altered rock and particle size analysis of slip zone soil
天然含水率% 湿密度/（g·cm−3） 干密度/（g·cm−3） 塑限（WP）/% 液限（WL）/% 塑性指数（IP） 颗粒级配/% 矿物含量检测结果/% 粒径大小/mm % 15.0 2.1 1.8 19.9 62.4 42.5 <0.005 mm 16.0 蛇纹石 水菱镁矿 绿泥石 0.005～0.075 mm 25.3 0.075～2 mm 39.0 88 10 2 >2 mm 19.7
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表 3 岩土体物理力学参数取值表
Table 3. Values of physical and mechanical parameters of rock and soil mass
岩性 杨氏模量/MPa 泊松比 黏聚力/kPa 内摩擦角/（°） 天然密度/（g·cm−3） 天然 饱和 天然 饱和 滑坡堆积体 800 0.21 60.00 45.00 35.00 28.00 2.20 滑床 2810 0.20 460.00 400.00 40.00 30.00 2.50 蚀变岩条带 310 0.24 67.03 43.24 20.29 13.79 1.85
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