Evaluation Method of Railway Schemes Along Rivers in Risk Areas of Moraine-Dammed Lake Outburst
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摘要:
为建立青藏高原南缘冰碛湖溃决危险区铁路方案风险评价方法，首先，对青藏高原南缘74例冰碛湖溃决灾害实例溃决机制进行统计分析；在此基础上，针对冰碛湖溃决影响因素众多、关系复杂且具有高度不确定性的特点，利用多态贝叶斯网络建立了冰碛湖溃决概率预测模型；然后，以冰碛湖溃决危险区沿河线路工程为承灾体，综合冰碛湖溃决危险性评估与沿河线河谷地貌特征提出了各类风险区线路长度计算程式，建立了针对冰碛湖溃决危险性的铁路选线方案评价方法；最后，以中尼铁路跨喜马拉雅段的樟木、吉隆局部走向方案为例，说明评价方法的作业程式. 研究结果表明：樟木方案在冰碛湖分布区的线路长度小于吉隆方案，从选线角度属于线路短直方案，但樟木方案各风险区段线路总长超出吉隆方案约45%；从冰碛湖溃决风险角度，吉隆方案优于樟木方案.
Abstract:This study is aimed at risk assessments of railway schemes in moraine-dammed lake outburst risk areas in the southern Tibet Plateau. Based on the mechanism analysis of 74 outburst events in the study area, a multi-state Bayesian-Network prediction model is established considering the complex relationships among the influencing factors and high uncertainties of the outburst events. Taking the railway line engineering along rivers in moraine-dammed lake outburst risk areas as the hazard bearing body and combining the risk assessment of moraine-dammed lakes with geomorphological characteristics of the river valley, a calculation program of the railway scheme length in various risk areas and an evaluation system for railway schemes considering moraine-dammed lake outburst risk are proposed. In addition, the operation procedure of the proposed method is demonstrated taking the Zhangmu and Gyirong schemes of the China-Nepal railway as examples The results show that the Zhangmu scheme has a smaller route length in the moraine lake distribution area than the Gyirong scheme, and belongs to the short straight scheme from the perspective of route selection; however, the total length of the Zhangmu scheme in each risk area exceeds that of the Gyirong scheme by about 45%. Therefore, the Gyirong scheme is the better selection when considering the moraine lake outburst risk.
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Key words:
- moraine-dammedlake outburst /
- B-Ns /
- China–Nepal railway /
- risk assessment
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图 1 青藏高原南缘冰川、冰湖及冰碛湖溃决灾害分布
Figure 1. Distributions of glaciers, glacier lakes and moraine-dammed lake outburst events in the southern Tibet Plateau
图 3 基于B-Ns的冰湖溃决危险性评估程式
Figure 3. Risk assessment procedure for moraine-dammed lake outburst based on B-Ns method
图 4 各类风险区线路长度计算流程
Figure 4. Calculation process of the railway line length in different risk areas
图 5 吉隆、波曲流域危险冰碛湖与线路方案示意
Figure 5. Railway schemes and distribution of dangerous moraine-dammed lakes in the Gyirong and Poiqu river
表 1 青藏高原南缘冰碛湖主要溃决机制统计
Table 1. Main outburst mechanisms of the moraine-dammed lakes in the southern Tibet Plateau
冰碛湖主要溃决机制 案例数 占比/% （冰崩/冰滑坡）涌浪漫顶 46 74.2 （降雨/冰川融水）洪水漫顶 12 19.4 管涌 5 8.1 冰碛物坍塌 5 8.1 外界动力激发 1 1.6 
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表 2 根节点因素多区间状态划分标准
Table 2. Division of risk factors in multi-interval safety states for root nodes
二级指标变量 二级指标状态值 0 1 x1/（°） < 8 > 8 x2 < 0.11 > 0.11 x3/km > 1 < 1 x4 相对不发育 相对较发育 x5 < 0.23 > 0.23 x6/m > 60 < 60 x7 固结 松散 x8 未满水 满水 x9 < 0.20 > 0.20 x10/（°） < 20 > 20 x11 无/少量 丰富 x12 < 0.25g > 0.25g
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表 3 冰碛湖溃决根节点的先验概率
Table 3. Prior probabilities of root nodes of moraine-dammed lake outburst
节点 状态数量 先验概率 状态 1 状态 2 x1 2 0.524 0.476 x2 0.286 0.714 x3 0.625 0.375 x4 0.192 0.808 x5 0.632 0.368 x6 0.240 0.760 x7 0.823 0.177 x8 0.423 0.577 x9 0.577 0.423 x10 0.712 0.288 x11 0.481 0.519 x12 0.900 0.100
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表 4 中间节点y1的条件概率
Table 4. Conditional probabilities of node y1
x1 x2 x3 x4 x5 y1 0 1 2 0 0 0 0 0 1.0 0 0 0 0 0 0 1 1.0 0 0 0 0 0 1 0 1.0 0 0 0 0 0 1 1 0.2 0.8 0 0 0 1 0 0 1.0 0 0 0 0 1 0 1 0.2 0.8 0 $\vdots $ $\vdots $ $\vdots $ $\vdots $ $\vdots $ $\vdots $ $\vdots $ $\vdots $ 1 1 1 0 1 0 0.2 0.8 1 1 1 1 0 0 0.2 0.8 1 1 1 1 1 0 0 1.0
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表 5 铁路方案冰碛湖溃决危险性评价指标
Table 5. Evaluation indexes of railway schemes considering moraine-dammed lake outburst risk
指标名称 比选因素 流域指标 冰碛湖总数量/个 冰碛湖总面积/km2 历史冰碛湖溃决案例数/次 线路指标 冰碛湖分布区线路总长度/km 溃决高风险区段线路长度/km 溃决次高风险区段线路长度/km 溃决中风险区段线路长度/km
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表 6 吉隆、樟木线路方案比选表
Table 6. Comparison of the railway schemes in the Gyirong and Poiqu river basins
指标类型 比选因素 吉隆 樟木 流域指标 冰碛湖总数量/个 130 121 冰碛湖总面积/ km2 5.8 17.3 历史冰碛湖溃决次数/次 2 6 线路指标 冰碛湖分布区
线路长度/ km107.9 93.5 冰碛湖溃决高危险区段
线路长度/ km21.2 38.3 冰碛湖溃决次高危险区
段线路长度/ km54.1 132.0 冰碛湖溃决中危险区段
线路长度/ km10.5 54.1
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