大坝原址重建施工导流风险特性研究

随着中国后水电开发时代的到来，大坝重建工程逐渐增多。大坝重建工程导流系统一般由原工程建筑物和新建导流建筑物联合组成，导流系统的组成和功能的丰富化使导流系统约束和导流风险因素更加复杂，导流风险呈现显著的特异性。本文旨在探索大坝重建工程施工导流风险计算方法及其变化规律。在大坝重建工程导流系统分析的基础上，归纳主要致险因素和致险模式，研究建立上游水位、下泄流量、下游水位等致险模式的数学表达，综合建立大坝重建工程导流多维风险判别式。针对系统中的洪水不确定性，利用Gumbel-Hougaard Copula函数描述洪水峰量联合分布，同时考虑原工程控泄规则和导流泄水建筑物的运用规则，利用Monte-Carlo方法模拟导流度汛过程并计算水力要素，结合风险判别式建立大坝重建工程施工导流多维风险计算模型。定性风险分析说明，建筑物的功能和设计标准差异决定了大坝重建工程导流系统的多种致险模式并不完全相关，导流系统风险呈显著多维分布特征。由于风险特性与导流系统配置有关，针对将原大坝作为上游围堰，占用原工程泄流建筑物出口的典型重建工程导流系统，进行了导流风险计算。定量风险特性分析说明：导流风险存在从下游漫顶致险模式向原坝泄水致险模式的转移点，主导致险模式转移的驱动因素是导流系统的泄流量，转移点对应下游围堰可防范的风险上限。研究成果为大坝重建工程导流风险评价和方案优化提供了重要支撑。

Risk Feature Analysis of River Diversion for Dam Reconstruction on the Original Site

As the era of the post-hydropower in China comes,the dam reconstruction works are increasing.In general,the river diversion for dam reconstruction consist of some original dam structures and some newly built diversion structures.Hence,compared to the diversion system for a newly built dam,the constraints and risk sources are more complicated in the diversion system for dam reconstruction.In this study,we will explored the risk evaluation of river diversion and the risk characteristics evolution rules.Based on the comprehensive analysis of diversion system for dam reconstruction,the main risk factors and risk modes were summarized,and the expressions of risk patterns were built.Those patterns included the upstream water level risk pattern,the downstream water level risk pattern and the discharge risk pattern.Then the multi-dimension risk discriminant was built on the ground of above expressions.Aiming at the flood uncertainty in the system,using the Copula function to describe the joint distribution of the flood peak and volume as well as taking account of the flow discharge rules and the operating regulation of discharge structures,the multi-dimension risk analysis model was built by sampling the flood routing,calculating hydraulic elements and integrating them into risk discriminant with Monte-Carlo method.The qualitative analysis showed that the above risk patterns were not fully correlated because of the differences in function and design standards of diversion structures,and the risk ruled by multi-dimensional distribution.Since the risk feature was decided by specified configuration,a typical case was provided,which used the original dam as upstream cofferdam and blocks the discharge way as construction pit.The quantitative risk analysis showed that there was a dominant risk pattern shifting point,beside which the discharging risk pattern took over downstream water level risk pattern as dominant risk pattern.The driving factor was the discharge rate of diversion system,and the shifting point corresponds to the upper risk limit that downstream cofferdam could defend.The research can serve as references for diversion risk evaluation and diversion scheme optimization for a dam reconstruction.